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UNITEDSTATES
SECURITIESANDEXCHANGECOMMISSION
Washington,D.C.20549

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number 811-06502

Name of Fund: BlackRock MuniYield Investment Fund (MYF)

Fund Address: 100 Bellevue Parkway, Wilmington, DE 19809

Name and address of agent for service: Anne F. Ackerley, Chief Executive Officer, BlackRock
MuniYield Investment Fund, 55 East 52nd Street, New York, NY 10055.

Registrant’s telephone number, including area code: (800) 882-0052, Option 4

Date of fiscal year end: 07/31/2010

Date of reporting period: 10/31/2009

Item 1 – Schedule of Investments

BlackRock MuniYield Investment Fund (MYF)       
Schedule of Investments October 31, 2009 (Unaudited)  (Percentages shown are based on Net Assets) 
      Par   
 State  Municipal Bonds    (000)  Value 
 California - 10.4%  California Health Facilities Financing Authority, California, RB, Catholic     
  Healthcare West, Series A, 6.00%, 7/01/39    $ 710 $  742,241 
  California Health Facilities Financing Authority, RB, Cedars-Sinai Medical     
  Center, 5.00%, 8/15/39             1,590  1,478,414 
  California Health Facilities Financing Authority, RB, Saint Joseph Health     
  System, Series A, 5.75%, 7/01/39             2,700  2,799,063 
  California State Public Works Board, RB, Department General Services,     
  Buildings 8 & 9, Series A, 6.25%, 4/01/34             4,525  4,694,190 
  Los Angeles Department of Water & Power, RB, Power System, Sub-Series     
  A 1, 5.25%, 7/01/38             3,300  3,471,006 
  San Diego Regional Building Authority, California, RB, County Operations     
  Center & Annex, Series A, 5.38%, 2/01/36             3,310  3,410,657 
  San Francisco City & County Airports Commission, Refunding RB,     
  2nd Series A-3, AMT, 6.75%, 5/01/34             2,500  2,648,900 
        19,244,471 
 Colorado - 3.4%  City & County of Denver, Colorado, Refunding RB, Series A,     
  5.25%, 11/15/36             4,050  4,026,712 
  Colorado Health Facilities Authority, Refunding RB, Catholic Healthcare,     
  Series A, 5.50%, 7/01/34 (a)             2,150  2,190,183 
        6,216,895 
 District of Columbia -  District of Columbia Water & Sewer Authority, RB, Series A,     
 1.2%  5.25%, 10/01/29             2,000  2,119,680 
 Florida - 35.1%  Broward County Educational Facilities Authority, RB, Educational     
  Facilities, Nova Southeastern (AGC), 5.00%, 4/01/31             2,210  2,215,923 
  City of Jacksonville, Florida, RB, Series B (MBIA), 5.13%, 10/01/32           1,500  1,494,930 
  City of Jacksonville, Florida, Refunding RB & Improvement (MBIA), 5.25%,     
  10/01/32             2,315  2,337,942 
  City of Miami Beach, Florida, RB, Water and Sewer (AMBAC), 5.75%,     
  9/01/25             3,000  3,089,400 
  City of Port Saint Lucie, Florida, RB (MBIA), 5.25%, 9/01/25           1,215  1,236,165 
  County of Broward, Florida, RB, Series I, AMT (AMBAC),     
  5.75%, 10/01/18             2,870  2,947,490 
  County of Hillsborough, Florida, RB (AMBAC), 5.40%, 11/01/12 (b)           1,055  1,189,502 

Portfolio Abbreviations
To simplify the listings of portfolio holdings in the Schedule of Investments, the names and descriptions of many of the securities
have been abbreviated according to the following list.

AGC  Assured Guaranty Corp.  GO  General Obligation Bonds 
AMBAC  American Municipal Bond Assurance Corp.  HFA  Housing Finance Agency 
AMT  Alternative Minimum Tax (subject to)  IDA  Industrial Development Authority 
ARB  Airport Revenue Bond  ISD  Independent School District 
CIFG  CDC IXIS Financial Guaranty  MBIA  Municipal Bond Investors Assurance 
COP  Certificates of Participation    (National Public Finance Guaranty Corp.) 
EDA  Economic Development Authority  RB  Revenue Bonds 
FSA  Financial Security Assurance Inc.  S/F  Single-Family 
GNMA  Government National Mortgage Association     

1

BlackRock MuniYield Investment Fund (MYF)       
Schedule of Investments October 31, 2009 (Unaudited)  (Percentages shown are based on Net Assets) 
      Par   
 State  Municipal Bonds    (000)  Value 
  County of Miami-Dade, Florida, RB, Miami International Airport, Series A,     
  AMT (FSA), 5.25%, 10/01/41    $ 1,800  $ 1,748,646 
  County of Miami-Dade, Florida, RB, Miami International Airport, Series A,     
  AMT (FSA), 5.50%, 10/01/41    2,930  2,942,365 
  County of Miami-Dade, Florida, RB, Miami International Airport, Series A,     
  AMT (MBIA), 6.00%, 10/01/29    3,275  3,315,807 
  County of Miami-Dade, Florida, RB, Series A, AMT (FSA),     
  5.00%, 10/01/33    2,625  2,471,359 
  County of Orange, Florida, Refunding RB (AMBAC), 5.00%, 10/01/29  1,750  1,782,217 
  County of Osceola, Florida, RB, Series A (MBIA), 5.50%, 10/01/27  1,760  1,794,074 
  County of Palm Beach, Florida, RB (MBIA), 7.20%, 6/01/15  3,340  3,989,463 
  County of Sumter, Florida, RB (AMBAC), 5.00%, 6/01/26  2,190  2,229,245 
  County of Sumter, Florida, RB (AMBAC), 5.00%, 6/01/30  2,475  2,488,687 
  Duval County HFA, RB, AMT (GNMA), 5.40%, 10/01/21    645  634,190 
  Florida Housing Finance Corp., RB, Homeowner Mortgage, Series 4, AMT     
  (FSA), 6.25%, 7/01/22    355  362,441 
  Florida Municipal Loan Council, RB, Series A-1 (MBIA),       
  5.13%, 7/01/34    1,580  1,544,197 
  Florida Municipal Loan Council, RB, Series B (MBIA), 5.38%, 11/01/30  4,250  4,269,592 
  Hillsborough County Aviation Authority, Florida, RB, Series C, AMT (AGC),     
  5.75%, 10/01/26    1,000  1,033,760 
  Hillsborough County IDA, RB, National Gypsum, Series A, AMT, 7.13%,     
  4/01/30    2,500  1,723,925 
  Hillsborough County IDA, RB, National Gypsum, Series B, AMT, 7.13%,     
  4/01/30    3,750  2,585,888 
  Lee County HFA, RB, Multi-County Program, Series A-1, AMT (GNMA),     
  7.13%, 3/01/28    30  30,459 
  Manatee County HFA, Refunding RB, S/F, Sub-Series 1, AMT (GNMA),     
  6.25%, 11/01/28    100  102,003 
  Martin County Health Facilities Authority, RB, Martin Memorial Medical     
  Center, Series A, 5.75%, 11/15/12 (b)    1,350  1,542,874 
  Martin County Health Facilities Authority, RB, Martin Memorial Medical     
  Center, Series A, 5.88%, 11/15/12 (b)    1,535  1,760,016 
  Miami-Dade County HFA, Florida, RB, Home Ownership Mortgage,     
  Series A-1, AMT (GNMA), 6.30%, 10/01/20    365  372,424 
  Orlando & Orange County Expressway Authority, RB, Series B (AMBAC),     
  5.00%, 7/01/30    250  251,982 
  Pinellas County HFA, RB, Multi-County Program, Series A-1, AMT (GNMA),     
  6.30%, 9/01/20    240  244,882 
  Pinellas County HFA, RB, Multi-County Program, Series A-1, AMT (GNMA),     
  6.35%, 9/01/25    340  347,021 
  Santa Rosa County School Board, COP, Series 2 (MBIA), 5.25%, 2/01/26  1,180  1,223,778 
  South Lake County Hospital District, RB, South Lake Hospital Inc., 6.38%,     
  10/01/34    1,150  1,151,300 
  Village Center Community Development District Recreational Revenue,     
  RB, Series A (MBIA), 5.38%, 11/01/34    1,995  1,827,360 

2

BlackRock MuniYield Investment Fund (MYF)       
Schedule of Investments October 31, 2009 (Unaudited)  (Percentages shown are based on Net Assets) 
      Par   
 State  Municipal Bonds    (000)  Value 
  Village Center Community Development District Recreational Revenue,     
  RB, Series A (MBIA), 5.13%, 11/01/36  $ 1,000     $ 871,710 
  Village Center Community Development District Utility Revenue, RB     
  (MBIA), 5.13%, 10/01/28         5,040  4,876,754 
  Volusia County IDA, RB, Student Housing, Stetson University Project,     
  Series A (CIFG), 5.00%, 6/01/35         1,000  861,840 
        64,891,611 
 Georgia - 8.4%  City of Atlanta, Georgia, RB, General, Subordinate Lien, Series C (FSA),     
  5.00%, 1/01/33         3,270  3,303,648 
  County of Fulton, Georgia, RB (MBIA), 5.25%, 1/01/35         1,000  1,021,680 
  Metropolitan Atlanta Rapid Transit Authority, RB, 3rd Series,     
  5.00%, 7/01/39         4,815  4,918,378 
  Municipal Electric Authority of Georgia, RB, General Resolution Projects,     
  Sub-Series D, 6.00%, 1/01/23         5,600  6,308,400 
        15,552,106 
 Illinois - 2.4%  Illinois Finance Authority, RB, Northwestern Memorial Hospital, Series A,     
  6.00%, 8/15/39         4,160  4,478,614 
 Indiana - 2.6%  Indiana Municipal Power Agency, Indiana, RB, Indiana Muni Power Agency,     
  Series B, 6.00%, 1/01/39         4,525  4,854,194 
 Kansas - 1.8%  Kansas Development Finance Authority, RB, Adventist Health, 5.50%,     
  11/15/29         3,250  3,335,670 
 Kentucky - 3.6%  Louisville & Jefferson County Metropolitan Government Parking Authority,     
  RB, Series A, 5.75%, 12/01/34         3,200  3,467,008 
  Louisville & Jefferson County Metropolitan Government, RB, Jewish     
  Hospital Saint Mary's Healthcare, 6.13%, 2/01/37         2,955  3,087,857 
        6,554,865 
 Maine - 1.2%  Maine State Housing Authority, Maine, RB, Series C, AMT,       
  5.45%, 11/15/23         2,285  2,286,531 
 Massachusetts - 2.6%  Massachusetts HFA, Massachusetts, RB, Housing, Series F, AMT, 5.70%,     
  6/01/40         2,125  2,129,356 
  Massachusetts Health & Educational Facilities Authority, RB, Tufts     
  University, 5.38%, 8/15/38         1,500  1,606,710 
  Massachusetts State College Building Authority, RB, Series A,     
  5.50%, 5/01/39         1,000  1,047,470 
        4,783,536 
 Michigan - 3.4%  Michigan State Building Authority, Refunding RB, Facilities Program,     
  Series I, 6.00%, 10/15/38         1,250  1,325,450 
  Michigan State Hospital Finance Authority, Refunding RB, Hospital, Henry     
  Ford Health, 5.75%, 11/15/39 (a)         2,785  2,669,840 
  Royal Oak Hospital Finance Authority, Michigan, RB, William Beaumont     
  Hospital, 8.25%, 9/01/39         1,970  2,287,938 
        6,283,228 
 Nevada - 1.7%  City of Las Vegas, Nevada, GO, Limited Tax, Performing Arts Center,     
  6.00%, 4/01/34         2,850  3,108,837 

3

BlackRock MuniYield Investment Fund (MYF)       
Schedule of Investments October 31, 2009 (Unaudited)  (Percentages shown are based on Net Assets) 
      Par   
 State  Municipal Bonds    (000)  Value 
 New Jersey - 4.0%  New Jersey EDA, Refunding RB, New Jersey American Water Co., Series A,     
  AMT, 5.70%, 10/01/39    $ 2,250 $  2,200,275 
  New Jersey State Housing & Mortgage Finance Agency, RB, S/F Housing,     
  Series CC, 5.25%, 10/01/29 (a)    2,290  2,355,013 
  New Jersey Transportation Trust Fund Authority, New Jersey, RB,     
  Transportation System, Series A, 5.88%, 12/15/38    2,670  2,888,112 
        7,443,400 
 New York - 7.3%  Long Island Power Authority, RB, Series A, 5.50%, 4/01/24  1,600  1,725,504 
  New York City Transitional Finance Authority, RB, Fiscal 2009, Series S-3,     
  5.25%, 1/15/39    2,500  2,595,950 
  New York State Dormitory Authority, RB, Education, Series B,     
  5.25%, 3/15/38    5,700  5,966,019 
  Triborough Bridge & Tunnel Authority, New York, RB, General, Series A-2,     
  5.38%, 11/15/38    3,030  3,227,405 
        13,514,878 
 North Carolina - 2.2%  North Carolina Eastern Municipal Power Agency, North Carolina, RB,     
  Series B, 5.00%, 1/01/26    885  901,231 
  North Carolina Medical Care Commission, RB, Duke University Health     
  System, Series A, 5.00%, 6/01/42 (a)    2,660  2,609,540 
  North Carolina Municipal Power Agency, RB, No. 1 Catawba, North     
  Carolina, Series A, 5.00%, 1/01/30    630  635,494 
        4,146,265 
 Ohio - 1.0%  Ohio Air Quality Development Authority, RB, Ohio Valley Electric Corp.,     
  5.63%, 10/01/19    1,910  1,904,308 
 Pennsylvania - 3.7%  Pennsylvania Economic Development Financing Authority, RB,     
  Pennsylvania, American Water Co. Project, 6.20%, 4/01/39  1,075  1,145,961 
  Pennsylvania Turnpike Commission, RB, Sub-Series B,       
  5.25%, 6/01/39    5,650  5,621,128 
        6,767,089 
 Puerto Rico - 4.0%  Puerto Rico HFA, RB, Sub-Capital Fund Modernization,       
  5.13%, 12/01/27    3,000  2,994,600 
  Puerto Rico Sales Tax Financing Corp., RB, First Sub-Series A, 5.75%,     
  8/01/37    4,200  4,345,320 
        7,339,920 
 Texas - 4.1%  Conroe ISD, Texas, GO, School Building, Series A, 5.75%, 2/15/35  1,800  1,937,376 
  Harris County Health Facilities Development Corp., Refunding RB,     
  Memorial Hermann Healthcare System, Series B, 7.25%, 12/01/35  800  894,160 
  Houston Texas Airport Systems Revenue, Refunding ARB, Senior Lien,     
  Series A, 5.50%, 7/01/39    1,170  1,213,571 
  Lower Colorado River Authority, Refunding RB, 5.75%, 5/15/28  1,620  1,699,688 
  North Texas Tollway Authority, Refunding RB, System, First Tier, Series K-     
  1 (AGC), 5.75%, 1/01/38    1,750  1,853,372 
        7,598,167 
 Utah - 1.2%  City of Riverton, Utah, RB, IHC Health Services Inc., 5.00%, 8/15/41 (a)  2,370  2,296,483 
 Virginia - 1.1%  Virginia Public School Authority, Virginia, RB, School Financing, 6.50%,     
  12/01/35    1,700  1,953,929 

4

BlackRock MuniYield Investment Fund (MYF)       
Schedule of Investments October 31, 2009 (Unaudited)  (Percentages shown are based on Net Assets) 
      Par   
 State  Municipal Bonds    (000)  Value 
 Wyoming - 1.4%  County of Sweetwater, Wyoming, Refunding RB, Idaho Power Co. Project,     
  5.25%, 7/15/26    $ 2,430 $  2,514,807 
  Total Municipal Bonds - 107.8%      199,189,484 
  Municipal Bonds Transferred to       
  Tender Option Bond Trusts (c)       
 California - 15.7%  Bay Area Toll Authority, Refunding RB, San Francisco Bay Area, Series F1,     
  5.63%, 4/01/44    2,680  2,886,730 
  California Educational Facilities Authority, RB, University of Southern     
  California, Series A, 5.25%, 10/01/39    4,200  4,426,002 
  Los Angeles Community College District, California, GO, Election of 2008,     
  Series A, 6.00%, 8/01/33    7,697  8,696,969 
  Los Angeles Unified School District, California, GO, Series I,     
  5.00%, 1/01/34    790  799,006 
  San Diego Public Facilities Financing Authority, Refunding RB, Series B,     
  5.50%, 8/01/39    8,415  8,942,957 
  University of California, RB, Series O, 5.75%, 5/15/34    3,000  3,317,670 
        29,069,334 
 District of Columbia -  District of Columbia, RB, Series A, 5.50%, 12/01/30    2,805  3,087,660 
 3.7%  District of Columbia, Water & Sewer Authority, RB, Series A, 5.50%,     
  10/01/39    3,507  3,744,279 
        6,831,939 
   Florida - 14.2%  City of Jacksonville, Florida, RB, Better Jacksonville (MBIA), 5.00%,     
  10/01/27    2,700  2,757,645 
  Hillsborough County Aviation Authority, Florida, RB, Series A, AMT (AGC),     
  5.50%, 10/01/38    3,869  3,890,360 
  Jacksonville Electric Authority, RB, River Power Park, Issue Three Series     
  Two, 5.00%, 10/01/37    2,100  2,102,625 
  Lee County HFA, RB, Multi-County Program, Series A-2, AMT (GNMA),     
  6.00%, 9/01/40    2,250  2,413,890 
  Manatee County HFA, RB, Series A, AMT (GNMA), 5.90%, 9/01/40  1,141  1,161,883 
  Polk County School Board, COP, Master Lease, Series A (FSA), 5.50%,     
  1/01/25    4,380  4,510,130 
  South Broward Hospital District, Florida, RB (MBIA), 5.63%, 5/01/12 (c)  8,500  9,468,320 
        26,304,853 
 Illinois - 4.3%  Illinois Finance Authority, RB, University of Chicago, Series B, 6.25%,     
  7/01/38    5,300  5,995,890 
  Illinois State Toll Highway Authority, RB, Series B, 5.50%, 1/01/33  1,750  1,870,568 
        7,866,458 
 Nevada - 6.3%  Clark County Water Reclamation District, GO, Limited Tax, 6.00%,     
  7/01/38    5,000  5,487,950 
  Clark County Water Reclamation District, GO, Series B, 5.50%,     
  7/01/29    5,668  6,159,402 
        11,647,352 
 New Hampshire - 1.3%  New Hampshire Health & Education Facilities Authority, Refunding RB,     
  Dartmouth College, 5.25%, 6/01/39    2,159  2,309,904 
 New York - 1.5%  New York City Municipal Water Finance Authority, RB, Series FF-2, 5.50%,     
  6/15/40    2,504  2,714,600 

5

BlackRock MuniYield Investment Fund (MYF)       
Schedule of Investments October 31, 2009 (Unaudited)  (Percentages shown are based on Net Assets) 
      Par   
 State  Municipal Bonds Transferred to Tender Option Bond Trusts (c)  (000)   Value 
 South Carolina - 1.9%  South Carolina State Public Service Authority, RB, Santee Cooper, Series     
  A, 5.50%, 1/01/38    $ 3,240 $  3,460,935 
 Texas - 5.3%  City of San Antonio, Texas, Refunding RB, Series A, 5.25%, 2/01/31  3,989  4,210,139 
  Harris County Cultural Education Facilities Finance Corp., RB, Hospital,     
  Texas Children's Hospital Project, 5.50%, 10/01/39    5,400  5,562,054 
        9,772,193 
 Virginia - 1.0%  Fairfax County IDA, Virginia, Refunding RB, Health Care, Inova Health     
  System, Series A, 5.50%, 5/15/35    1,749  1,836,154 
 Wisconsin - 1.7%  Wisconsin Health & Educational Facilities Authority, Refunding RB,     
  Froedtert & Community Health Inc., 5.25%, 4/01/39    3,290  3,231,387 
  Total Municipal Bonds Transferred to       
  Tender Option Bond Trusts - 56.9%      105,045,109 
  Total Long-Term Investments       
  (Cost - $294,445,739) - 164.7%      304,234,593 
  Short-Term Securities    Shares   
  FFI Institutional Tax-Exempt Fund, 0.32% (d)(e)    2,600,000  2,600,000 
  Total Short-Term Securities       
  (Cost - $2,600,000) - 1.4%      2,600,000 
  Total Investments (Cost - $297,045,739*) - 166.1%      306,834,593 
  Liabilities in Excess of Other Assets - (3.6)%      (6,634,762) 
  Liability for Trust Certificates, Including       
  Interest Expense and Fees Payable - (30.3)%      (56,038,947) 
  Preferred Shares, at Redemption Value - (32.2)%      (59,480,541) 
  Net Assets Applicable to Common Shares - 100.0%    $ 184,680,343 

* The cost and unrealized appreciation (depreciation) of investments as of October 31, 2009,

  as computed for federal income tax purposes, were as follows: 
  Aggregate cost  $ 242,144,800 
  Gross unrealized appreciation  $ 13,452,100 
  Gross unrealized depreciation    (4,754,951) 
  Net unrealized appreciation  $ 8,697,149 
(a)  When-issued security.     
      Unrealized 
      Appreciation 
  Counterparty  Market Value  (Depreciation) 
  Citigroup NA  $ 5,279,380 $  (35,339) 
  JPMorgan Chase Bank NA  $ 2,296,483  (36,238) 
  Merrill Lynch & Co.  $ 2,355,013  1,214 
  Morgan Stanley Capital     
  Securities Inc.  $ 2,190,183  (16,276) 

(b) US government securities, held in escrow, are used to pay interest on this security as well as to retire the bond in full at
the date indicated, typically at a premium to par.
(c) Securities represent bonds transferred to a tender option bond trust in exchange for which the Fund
acquired residual interest certificates. These securities serve as collateral in a financing transaction.

6

BlackRock MuniYield Investment Fund (MYF)
Schedule of Investments October 31, 2009 (Unaudited)

(d) Investments in companies considered to be an affiliate of the Fund, for purposes of Section 2(a)(3) of the Investment
Company Act of 1940, were as follows:

  Net     
Affiliate  Activity  Income    
FFI Institutional Tax-Exempt       
Fund  $ 1,199,949  $ 4,490 

(e) Represents the current yield as of report date.
Ÿ Fair Value Measurements - Various inputs are used in determining the fair value of investments, which are as follows:

Ÿ Level 1 - price quotations in active markets/exchanges for identical assets and liabilities
Ÿ Level 2 - other observable inputs (including, but not limited to: quoted prices for similar assets or liabilities in
markets that are active, quoted prices for identical or similar assets or liabilities in markets that are not active,
inputs other than quoted prices that are observable for the assets or liabilities (such as interest rates, yield curves,
volatilities, prepayment speeds, loss severities, credit risks and default rates) or other market-corroborated inputs)

Ÿ Level 3 - unobservable inputs based on the best information available in the circumstances, to the extent
observable inputs are not available (including the Fund's own assumptions used in determining the fair value of
investments)

The inputs or methodology used for valuing securities are not necessarily an indication of the risk associated with
investing in those securities. For information about the Fund's policy regarding valuation of investments and other
significant accounting policies, please refer to the Fund's most recent financial statements as contained in its semi-
annual report.
The following table summarizes the inputs used as of October 31, 2009 in determining the fair valuation of the Fund's
investments:

  Investments in 
Valuation Inputs  Securities 
  Assets 
Level 1 - Short-Term Securities  $ 2,600,000 
Level 2 - Long-Term Investments1  304,234,593 
Level 3  - 
Total  $ 306,834,593 

1 See above Schedule of Investments for values in each state or political subdivision.

7

Item 2 – Controls and Procedures

2(a) – The registrant's principal executive and principal financial officers or persons performing
similar functions have concluded that the registrant's disclosure controls and procedures (as
defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the
“1940 Act”)) are effective as of a date within 90 days of the filing of this report based on the
evaluation of these controls and procedures required by Rule 30a-3(b) under the 1940 Act
and Rule 13(a)-15(b) under the Securities Exchange Act of 1934, as amended.

2(b) – There were no changes in the registrant's internal control over financial reporting (as defined
in Rule 30a-3(d) under the 1940 Act) that occurred during the registrant's last fiscal quarter
that have materially affected, or are reasonably likely to materially affect, the registrant's
internal control over financial reporting.

Item 3 – Exhibits

Certifications – Attached hereto

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment
Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by
the undersigned, thereunto duly authorized.

BlackRock MuniYield Investment Fund

By: /s/ Anne F. Ackerley
Anne F. Ackerley
Chief Executive Officer of
BlackRock MuniYield Investment Fund

Date: December 18, 2009

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment
Company Act of 1940, this report has been signed below by the following persons on behalf
of the registrant and in the capacities and on the dates indicated.

By: /s/ Anne F. Ackerley
Anne F. Ackerley
Chief Executive Officer (principal executive officer) of
BlackRock MuniYield Investment Fund

Date: December 18, 2009

By: /s/ Neal J. Andrews
Neal J. Andrews
Chief Financial Officer (principal financial officer) of
BlackRock MuniYield Investment Fund

Date: December 18, 2009