--------------------------------------------------------------------------------


                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549



                                    FORM 11-K




     (Mark One)

         [X]        ANNUAL REPORT PURSUANT TO SECTION 15(D) OF

                       THE SECURITIES EXCHANGE ACT OF 1934

                   For The Fiscal Year Ended December 31, 2004


                                       OR


         [ ]       TRANSITION REPORT PURSUANT TO SECTION 15(D) OF

                       THE SECURITIES EXCHANGE ACT OF 1934

                 For the transition period from _____ to _____.


                          COMMISSION FILE NO: 001-13739



         A. Full title of the plan and the address of the plan, if different
from that of the issuer named below:


                    TUCSON ELECTRIC POWER COMPANY 401(K) PLAN


         B. Name of issuer of the securities held pursuant to the plan and the
address of its principal executive office:


                          UniSource Energy Corporation
                       One South Church Avenue, Suite 100
                                Tucson, AZ 85701


--------------------------------------------------------------------------------





TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
INDEX
--------------------------------------------------------------------------------
DECEMBER 31, 2004 AND 2003

                                                                         PAGE(S)

Required Information...........................................................3

Report of Independent Registered Public Accounting Firm........................4

FINANCIAL STATEMENTS

Statements of Net Assets Available for Benefits................................5

Statements of Changes in Net Assets Available for Benefits.....................6

Notes to Financial Statements...............................................7-11

SUPPLEMENTAL SCHEDULES

Schedule H, Line 4(i) - Schedule of Assets (Held at End of Year)...........13-14

Signature Page................................................................15

Exhibit 23 - Consent of Independent Registered Public Accounting Firm.........16


Note:    Other schedules required by Section 2520.103-10 of the Department of
         Labor's Rules and Regulations for Reporting and Disclosure under the
         Employee Retirement Income Security Act of 1974 have been omitted
         because they are not applicable.





                              REQUIRED INFORMATION


         The Tucson Electric Power Company 401(k) Plan (the Plan) is subject to
the Employee Retirement Income Security Act of 1974 (ERISA). Therefore, in lieu
of the requirements of Items 1 - 3 of Form 11-K, the financial statements and
schedules of the Plan for the fiscal year ended December 31, 2004, which have
been prepared in accordance with the financial reporting requirements of ERISA,
are filed herewith and incorporated herein by this reference.

         The written consent of PricewaterhouseCoopers LLP with respect to the
annual financial statements of the Plan is filed as Exhibit 23 to this Annual
Report.


                                       3



             REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM


To the Participants and Administrator of the
Tucson Electric Power Company 401 (k) Plan:

In our opinion, the accompanying statements of net assets available for benefits
and the related statements of changes in net assets available for benefits
present fairly, in all material respects, the net assets available for benefits
of the Tucson Electric Power Company 401 (k) Plan (the "Plan") at December 31,
2004 and December 31, 2003, and the changes in net assets available for benefits
for the years then ended in conformity with accounting principles generally
accepted in the United States of America. These financial statements are the
responsibility of the Plan's management. Our responsibility is to express an
opinion on these financial statements based on our audits. We conducted our
audits of these statements in accordance with the standards of the Public
Company Accounting Oversight Board (United States). Those standards require that
we plan and perform the audit to obtain reasonable assurance about whether the
financial statements are free of material misstatement. An audit includes
examining, on a test basis, evidence supporting the amounts and disclosures in
the financial statements, assessing the accounting principles used and
significant estimates made by management, and evaluating the overall financial
statement presentation. We believe that our audits provide a reasonable basis
for our opinion.

Our audits were conducted for the purpose of forming an opinion on the basic
financial statements taken as a whole. The supplemental schedule of assets (held
at end of year) is presented for the purpose of additional analysis and is not a
required part of the basic financial statements but is supplementary information
required by the Department of Labor's Rules and Regulations for Reporting and
Disclosure under the Employee Retirement Income Security Act of 1974. These
supplemental schedules are the responsibility of the Plan's management. The
supplemental schedules have been subjected to the auditing procedures applied in
the audits of the basic financial statements and, in our opinion, are fairly
stated in all material respects in relation to the basic financial statements
taken as a whole.


/s/ PricewaterhouseCoopers LLP
------------------------------

PricewaterhouseCoopers LLP
Los Angeles, CA
June 27, 2005


                                       4



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS
DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------



                                                      2004          2003
ASSETS

                                                                    
Investment:                                       $137,015,679   $121,155,621
                                                  ------------   ------------


Receivables:
     Employer contributions                            122,682         92,651
     Participant contributions                         246,495        206,410
     Due from broker for securities sold                21,051             --
                                                  ------------   ------------

          Total receivables                            390,228        299,061
                                                  ------------   ------------

          Net assets available for benefits       $137,405,907   $121,454,682
                                                  ============   ============





              The accompanying notes are an integral part of these
                             financial statements.



                                       5



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS
YEARS ENDED DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------



                                                                  2004               2003
                                                                          
ADDITIONS TO NET ASSETS ATTRIBUTED TO:

   Investment income:
      Interest and dividend income                            $    490,779      $    459,113
      Net appreciation in fair value of investments             10,212,694        21,472,737
                                                              ------------      ------------

          Total investment income                               10,703,473        21,931,850
                                                              ------------      ------------
   Contributions:
      Employer contributions                                     3,669,184         3,274,061
      Participant contributions                                  8,044,632         6,868,251
      Participant rollovers                                        671,420         6,114,968
                                                              ------------      ------------
          Total contributions                                   12,385,236        16,257,280
                                                              ------------      ------------
          Total additions                                       23,088,709        38,189,130
                                                              ------------      ------------
DEDUCTIONS FROM NET ASSETS ATTRIBUTED TO:

   Benefits paid to participants                                 7,123,951         6,127,855
   Administrative expenses                                          13,533            11,503
                                                              ------------      ------------
          Total deductions                                       7,137,484         6,139,358


Net increase                                                    15,951,225        32,049,772
                                                              ------------      ------------
NET ASSETS AVAILABLE FOR BENEFITS:

   Beginning of year                                           121,454,682        89,404,910
                                                              ------------      ------------
   End of year                                                $137,405,907      $121,454,682
                                                              ============      ============




              The accompanying notes are an integral part of these
                              financial statements.


                                       6



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------


1.   DESCRIPTION OF PLAN

     The following description of the Tucson Electric Power Company 401(k) Plan
     (the "Plan") provides only general information. Participants should refer
     to the Plan agreement for a more complete description of the Plan's
     provisions.

     GENERAL
     All regular employees of Tucson Electric Power Company and participating
     subsidiaries of UniSource Energy Corporation, the parent company of the
     Plan sponsor, (collectively, the "Company"), who are employed by the
     Company on or after November 1, 1985 are eligible to participate. The Plan
     is subject to the provisions of the Employee Retirement Income Security Act
     of 1974 ("ERISA").

     ADMINISTRATION
     The Company's Pension Committee (the "Committee"), comprised of three or
     more employees, administers the Plan. Fidelity Management Trust Company
     (the "Trustee") serves as trustee of all Plan investments. Fidelity
     Investments Institutional Operations Company, Inc. serves as recordkeeper
     for the Plan. The Company funds the Plan's administrative costs, except for
     loan administrative fees and brokerage account fees, which are paid
     directly by the participants out of their accounts.

     CONTRIBUTIONS
     Upon admission to the Plan, participants may contribute, by way of payroll
     deductions, a percentage up to but not in excess of 15% of their pre-tax
     compensation. Participants may direct their contributions to be invested
     entirely into any one of the individual investment funds or, in multiples
     of 1% into any combination of these funds. Contributions are subject to
     certain limitations.

     The Plan also allows for rollovers from participants' other external 401(k)
     plans ("Qualified Rollovers") into the Plan. Qualified Rollovers are
     accounted for as participant contributions in a separate account of the
     participant, and are directed in the same manner as discussed above for
     participant contributions.

     Each payroll period during the two years ended December 31, 2004, the
     Company contributed Company Matching Contributions to the Plan with respect
     to each participant in an amount equal to the lesser of (i) the excess of
     the participant's Compensation Deferral Contributions to the Plan in the
     Plan Year over the Company Matching Contributions previously made in
     respect to the participant in the Plan year or (ii) 4.5% of the
     participant's compensation for that payroll period. Participants direct the
     investment of such Company contributions in the same manner as discussed
     above for participant contributions. Effective July 1, 2000, the Board of
     Directors of Tucson Electric Power Company has the discretion each year to
     establish the formula for Company Matching Contributions.

     LOANS TO PARTICIPANTS
     Loan amounts shall not exceed the lesser of $50,000 or 50% of the vested
     balance of the participant's accounts at the date of the loan. Loan terms
     must be for at least six months and no more than five years, except that
     loans used to purchase a principal residence may have a term up to 15
     years. Loan repayments are made every two weeks through payroll deductions
     and are considered to be in default if all payments are not made for any
     three month period. If a participant fails to repay a loan in full, the
     Committee may immediately reduce the value of the participant's account by
     the amount of unpaid principal and interest and/or reduce any distribution
     by the amount of the remaining unpaid principal and interest. Each loan is


                                       7



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------


     secured by the balance of the participant's account and bears a fixed rate
     of interest of the prime rate plus 2%. Interest rates for the years ended
     December 31, 2004 and 2003 ranged from 4.00% to 11.50%. Loan transactions
     are treated as a transfer to (from) the investment fund from (to) the
     Participant Loans fund.

     DISTRIBUTIONS
     A participant's account becomes distributable upon termination of
     employment, total disability, death or retirement. A participant or
     beneficiary of a deceased participant may elect to have his or her account
     distributed a) as soon as practicable following the date of termination or
     death, or b) in the plan year following such date. Absent such an election,
     distributions do not occur until the close of the quarter in which the last
     Company matching contribution is made.

     The amount distributable to a participant or beneficiary is equal to the
     balance in the account valued as of the most recent date preceding such
     distribution as the Trustee can determine. Benefits payable to a
     participant or the beneficiary are paid in a cash lump sum.

     Under certain conditions, once each plan year a participant may withdraw
     all or a portion of his or her account while still employed by the Company.
     Withdrawals from a participant's account are only permitted (i) for
     participants who have attained age 59-1/2 or (ii) in the event of a
     participant's hardship as defined in Section 401(k) of the Internal Revenue
     Code of 1954, as amended. Beginning with the plan year in which
     participants reach age 59-1/2, they may withdraw any portion up to the
     entire amount of their Salary Deferral Contributions Account and/or their
     Company Matching Contributions Account. In addition, participants may
     withdraw any portion of their Salary Deferral Contributions Account,
     excluding earnings credited after December 31, 1988, if they have incurred
     a financial hardship. The amount which may be withdrawn in the case of a
     participant's hardship may not exceed the amount needed and is subject to
     the approval of the Committee.

     INVESTMENTS
     Participants may direct the investment of their Pretax Contributions and
     Company Matching Contributions in a variety of investment vehicles
     comprised of common stocks, mutual funds, money market funds and
     common/collective funds. The Plan is intended to comply with Section 404(c)
     of ERISA.

     VESTING
     A participant's interest in each of his accounts is at all times 100%
     vested.

     PLAN TERMINATION
     Although it has not expressed any intent to do so, the Company has the
     right under the Plan to terminate the Plan. Upon termination of the Plan,
     the accounts under the Plan will be valued and distributed to participants
     at the time of such termination, subject to the provisions of ERISA.

2.   ACQUISITION

     On August 11, 2003, UniSource Energy completed the purchase of the Arizona
     electric and gas utility businesses from Citizens Communications Company
     (Citizens). Upon closing and transfer of employment to UniSource Energy
     Services, Inc., the participants of the Citizens' 401(k) Savings Plan were
     allowed to roll over their account balance, including outstanding loan


                                       8



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------


     balances, to the Tucson Electric Power Company 401(k) Plan. Rollovers from
     the Citizens Plan of $5,986,061 are included in 2003 participant rollovers.

3.   SUMMARY OF ACCOUNTING POLICIES

     BASIS OF ACCOUNTING
     The financial statements of the Plan are prepared using the accrual basis
     of accounting and in accordance with accounting principles generally
     accepted in the United States of America.

     USE OF ESTIMATES
     The preparation of financial statements in conformity with generally
     accepted accounting principles requires management to make estimates and
     assumptions that affect the reported amounts of assets and liabilities and
     changes therein, and disclosure of contingent assets and liabilities.
     Actual results could differ from those estimates.

     INVESTMENT VALUATION AND INCOME RECOGNITION
     Plan investments other than the Fidelity Managed Income Portfolio, are
     presented at fair value. The fair values of common stock, mutual funds and
     common/collective fund shares are based upon the closing market price on
     the valuation date. Investments in the Fidelity Managed Income Portfolio
     are valued based upon the net asset value of the unit value of each
     specific fund. Participant loans are valued at cost, which approximates
     fair value.

     Security transactions are recorded on the trade date basis. Expenses paid
     by the Plan in connection with such transactions include brokerage
     commissions and taxes that are included in the cost of securities purchased
     and deducted from the proceeds of securities sold. Net appreciation
     (depreciation) in the fair value of the Plan's investments consists of the
     realized gains (losses) and the unrealized appreciation (depreciation) on
     those investments. Dividend income is recognized on the ex-dividend date.
     Interest income is recognized as earned. Employer and Participant
     contributions are recognized on the accrual basis.

     PAYMENT OF BENEFITS
     Benefits are recorded when paid. Net assets available for benefits of
     $29,963 at December 31, 2004 are due to participants who have withdrawn
     from participation in the Plan.

4.   INVESTMENTS

     The following investments represent 5% or more of the Plan's net assets as
of December 31:



                                                              2004               2003

                                                                       
   Fidelity Growth Company Fund
         533,412 and 542,172 units, respectively          $29,908,412        $27,146,554

   Fidelity Magellan Fund
        255,162 and 258,840 units, respectively           $26,483,275        $25,298,986

   Fidelity Equity Income Fund
        355,352 and 330,876 units, respectively           $18,755,502        $16,461,069


                                       9



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------


   Fidelity Retirement Money Market Fund
        12,126,473 and 12,146,654 units, respectively     $12,126,473        $12,146,654

   Fidelity Low Priced Stock Fund
        247,534 and 191,768 units, respectively           $ 9,963,258        $ 6,708,029

   Fidelity Managed Income Portfolio
        7,196,002 and 5,968,993 units, respectively       $ 7,196,002        $ 5,968,993

   Fidelity Intermediate Bond Fund
        655,130 and 619,266 units, respectively           $ 6,891,963        $ 6,601,380




     During 2004 and 2003 the Plan's investments appreciated (including gains
     and losses on investments purchased and sold, as well as held during the
     year) in value by $10,212,694 and $21,472,737 as follows:



                                           2004                  2003

                                                                
     Mutual Funds                      $ 10,275,573          $ 20,550,764
     Common Stock                           (62,879)              921,973
                                       ------------          ------------
          Total                        $ 10,212,694          $ 21,472,737
                                       ============          ============



5.   CONCENTRATION OF CREDIT RISK

     At December 31, 2004 and 2003, the Plan's assets consist primarily of
     investments in financial instruments, money market funds, investment
     contracts, mutual funds, UniSource Energy Corporation stock and participant
     loans. Investment securities are exposed to various risks such as interest
     rate, market, and credit risks. Due to the level of risk associated with
     certain investment securities, it is at least reasonably possible that
     changes in the values of investment securities will occur in the near term
     and that such changes could materially affect participants' account
     balances and the amounts reported in the statement of net assets available
     for benefits.

6.   TAX STATUS

     The Plan is qualified under Section 401 of the Internal Revenue Code
     ("IRC") and is, therefore, considered to be exempt from federal income
     taxes under the provisions of Section 501(a). A tax qualification letter,
     dated September 27, 2002, has been received from the IRS. The Plan has
     since been amended; however, the Plan administrator believes that the Plan,
     as amended, is currently designed and being operated in compliance with the
     applicable requirements of the IRC. Therefore, no provision for income
     taxes has been included in the Plan's financial statements.

7.   RELATED PARTY TRANSACTIONS

     In 2004 and 2003, the Plan's investments in shares of mutual funds managed
     by the Trustee of $117,202,526 and $103,532,978, respectively, as well as
     in stock of UniSource Energy Corporation in the amounts of $2,638,328 and
     $2,866,040, respectively, qualify as party-in-interest transactions for
     which a statutory exemption exists.


                                       10



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2004 AND 2003
--------------------------------------------------------------------------------


     The Trustee invests in the Company's common stock in accordance with the
     provisions of the Plan. The following is a summary of transactions in the
     Company's common stock:




                                                    2004            2003

                                                                 
         Cost of shares purchased                $ 645,633       $ 764,754
         Number of shares purchased                 26,375          39,453

         Proceeds from shares sold               $ 810,466       $ 802,246
         Number of shares sold                      33,168          37,838



8.   RECONCILIATION OF FINANCIAL STATEMENTS TO FORM 5500

     The following reconciles net assets available for plan benefits per the
     financial statements at December 31, 2004 to Form 5500:



                                                                     2004
                                                                      
        Net assets available for benefits per the 
          financial statements                                  $137,405,907
        Amounts allocated to withdrawing participants
          at December 31, 2004                                       (29,963)
                                                                ------------
        Net assets available for benefits per Form 5500         $137,375,944
                                                                ============



     The following reconciles benefits paid to participants per the financial
     statements for the year ended December 31, 2004, to Form 5500:



                                                                    2004
                                                             
        Benefits paid to participants per the 
          financial statements                                  $ 7,123,951
        Add: Amounts allocated to withdrawing participants
          at December 31, 2004                                       29,963
                                                                -----------
        Benefits paid to participants per Form 5500             $ 7,153,914
                                                                ===========



     Amounts allocated to withdrawing participants are for benefit claims that
     have been processed and approved for payment prior to December 31, 2004,
     but not yet paid as of that date.



                                       11




                             SUPPLEMENTAL SCHEDULES



                                       12



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
SCHEDULE H, LINE 4(I) - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
DECEMBER 31, 2004
--------------------------------------------------------------------------------




                                                     DESCRIPTION OF INVESTMENT INCLUDING
           IDENTITY OF ISSUE, BORROWER,                MATURITY DATE, RATE OF INTEREST,
(a) (b)      LESSOR OR SIMILAR PARTY            (c)   COLLATERAL, PAR OR MATURITY VALUE           (d) COST**       (e) CURRENT VALUE
             -----------------------                  ---------------------------------               ------           -------------

                                                                                                                              
    *   Fidelity Growth Company Fund                Investment in 533,412 units of a growth fund                       $  29,908,412

    *   Fidelity Magellan Fund                      Investment in 255,162 units of a growth fund                          26,483,275

    *   Fidelity Equity Income Fund                 Investment in 355,352 units of a growth and
                                                      income fund                                                         18,755,502

    *   Fidelity Retirement Money Market            Investment in 12,126,473 units of a money
        Portfolio                                     market fund                                                         12,126,473

    *   Fidelity Low-Priced Stock Fund              Investment in 247,534  units of a growth fund                          9,963,258

    *   Fidelity Intermediate Bond Fund             Investment in 655,130 units of an income fund                          6,891,963

    *   Fidelity Managed Income Portfolio           Investment in 7,196,002 units of an open
                                                      ended commingled pool                                                7,196,002

        Spartan U.S. Equity Index Fund              Investment in 104,172 units of a growth fund                           4,464,819

    *   Fidelity Asset Manager Fund                 Investment in 261,135 units of an asset
                                                      allocation fund                                                      4,233,005

        Janus Worldwide Fund                        Investment in 73,008 units of a growth fund                            3,023,271

    *   UniSource Energy Stock Fund                 Investment in 109,429 units of a unitized
                                                       company stock fund                                                  2,638,328

        BrokerageLink Account                       Investment in 3,394,157  units of a self-
                                                      directed investment fund                                             3,394,157

        Janus Flexible Bond Fund                   Investment in 180,805 units of an  income fund                          1,753,812

    *   Fidelity Diversified International Fund     Investment in 13,260 units of a growth fund                              379,765

    *   Fidelity Freedom 2005                       Investment in 31,489 units of an income fund                             340,086

        American Beacon Small Cap Value Plan        Investment in 16,525 units of an growth fund                             329,006

    *   Fidelity Freedom 2010                       Investment in 23,404 units of an income fund                             318,756

        Franklin Utilities A                        Investment in 28,489 units of an growth and 
                                                      income fund                                                            315,948

    *   Fidelity Freedom 2015                       Investment in 24,063 units of an growth fund                             265,894

    *   Fidelity Freedom 2025                       Investment in 16,557 units of an growth fund                             186,766


                                       13



TUCSON ELECTRIC POWER COMPANY
401(K) PLAN
SCHEDULE H, LINE 4(I) - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
DECEMBER 31, 2004
--------------------------------------------------------------------------------



                                                     DESCRIPTION OF INVESTMENT INCLUDING
           IDENTITY OF ISSUE, BORROWER,                MATURITY DATE, RATE OF INTEREST,
(a) (b)      LESSOR OR SIMILAR PARTY            (c)   COLLATERAL, PAR OR MATURITY VALUE           (d) COST**       (e) CURRENT VALUE
             -----------------------                  ---------------------------------               ------           -------------

                                                                                                                              

    *   Fidelity Small Cap Stock                    Investment in 4,290 units of an growth fund                               77,897

    *   Fidelity Freedom 2020                       Investment in 1,586 units of an growth fund                               22,145

    *   Fidelity Freedom 2030                       Investment in 1,393 units of an growth fund                               19,620

    *   Fidelity Freedom 2035                       Investment in 1,661 units of an growth fund                               19,002

    *   Fidelity Freedom 2040                       Investment in 1,778 units of an growth fund                               14,705

    *   Loans to participants                       Loans with maturities ranging from 1 month to
                                                      180 months and interest rates from 4.00%
                                                      to 11.50%                                                           3,893,812
                                                                                                                       -------------
                                                                                                                       $ 137,015,679
                                                                                                                       =============



*   Denotes party-in-interest
**  Historical cost information is not required for participant-directed
    investments.


                                       14



                                   SIGNATURES


         The Plan. Pursuant to the requirements of the Securities Exchange Act
of 1934, the trustees (or other persons who administer the employee benefit
plan) have duly caused this annual report to be signed on its behalf by the
undersigned hereunto duly authorized.


TUCSON ELECTRIC POWER COMPANY 401(k) PLAN

By: Tucson Electric Power Company 401(k) Plan Administrative Committee




    By:   /s/   Kevin P. Larson                          Date: June 29, 2005
          ------------------------------------------           -------------
                Kevin P. Larson
          Member of Plan Administrative Committee



    By:   /s/   Steven J. Glaser                         Date: June 29, 2005
          ------------------------------------------           -------------
                Steven J. Glaser
          Member of Plan Administrative Committee



    By:   /s/   Michael J. DeConcini                     Date: June 29, 2005
          ------------------------------------------           -------------
                Michael J. DeConcini
          Member of Plan Administrative Committee


                                       15