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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: 07/31/2011

Date of reporting period: 10/31/2010

Item 1 – Schedule of Investments


Schedule of Investments October 31, 2010 (Unaudited)

BlackRock MuniYield Investment Fund (MYF)
(Percentages shown are based on Net Assets)

  Par   
Municipal Bonds  (000)  Value 
Arizona — 1.4%     
Maricopa County Pollution Control Corp.,     
Refunding RB, Southern California     
Edison Co., Series A, 5.00%, 6/01/35   $ 1,380  $ 1,410,540 
Pima County IDA, Refunding IDRB,     
Tucson Electric Power, 5.75%,     
9/01/29  1,230  1,271,057 
    2,681,597 
California — 16.6%     
California Health Facilities Financing     
Authority, Refunding RB, Series A:     
Catholic Healthcare West, 6.00%,     
7/01/39  710  772,956 
St. Joseph Health System, 5.75%,     
7/01/39  2,700  2,870,154 
California State Public Works Board, RB:     
Department of General Services,     
Buildings 8 & 9, Series A, 6.25%,     
4/01/34  4,525  4,887,136 
Various Capital Projects,     
Sub-Series I-1, 6.38%, 11/01/34  1,265  1,386,529 
Grossmont Union High School District,     
GO, Election of 2008, Series B,     
4.75%, 8/01/45  4,925  4,750,950 
Los Angeles Department of Airports,     
Refunding RB, Senior, Los Angeles     
International Airport, Series A, 5.00%,     
5/15/35  5,420  5,624,009 
Los Angeles Department of Water &     
Power, RB, Power System,     
Sub-Series A-1, 5.25%, 7/01/38  3,300  3,549,711 
San Diego Regional Building Authority     
California, RB, County Operations     
Center & Annex, Series A, 5.38%,     
2/01/36  3,310  3,559,607 
San Francisco City & County Airports     
Commission, Refunding RB, Second     
Series A-3, Mandatory Put Bonds,     
AMT, 6.75%, 5/01/19 (a)  2,500  2,575,850 
State of California, GO, Various Purpose,     
6.00%, 3/01/33  2,535  2,911,802 
    32,888,704 
Colorado — 2.2%     
City & County of Denver Colorado,     
Refunding RB, Series A, 5.25%,     
11/15/36  4,050  4,270,482 

 

    Par   
Municipal Bonds    (000)  Value 
District of Columbia — 1.1%       
District of Columbia Water & Sewer       
Authority, RB, Series A, 5.25%,       
10/01/29  $ 2,000  $ 2,183,860 
Florida — 10.1%       
City of Jacksonville Florida, RB, Series B     
(NPFGC), 5.13%, 10/01/32    1,500  1,540,905 
County of Miami-Dade Florida, RB,       
Miami International Airport, Series A,     
AMT:       
(AGM), 5.50%, 10/01/41    930  957,621 
(NPFGC), 6.00%, 10/01/29    3,275  3,311,385 
County of Osceola Florida, RB, Series A     
(NPFGC), 5.50%, 10/01/27    1,760  1,802,099 
County of Sumter Florida, RB (AMBAC),     
5.00%, 6/01/26    685  707,194 
Florida Housing Finance Corp.,       
Refunding RB, Homeowner Mortgage,     
Series 4, AMT (AGM), 6.25%,       
7/01/22    335  355,442 
Hillsborough County IDA, RB, AMT,       
National Gypsum Co.:       
Series A, 7.13%, 4/01/30    2,500  2,437,050 
Series B, 7.13%, 4/01/30    3,750  3,655,575 
Santa Rosa County School Board, COP,     
Refunding, Series 2 (NPFGC), 5.25%,     
2/01/26    1,180  1,252,086 
South Lake County Hospital District, RB,     
South Lake Hospital Inc., 6.38%,       
10/01/34    1,150  1,164,709 
Village Center Community Development     
District, RB, Series A (NPFGC):       
5.38%, 11/01/34    1,995  1,876,038 
5.13%, 11/01/36    1,000  901,880 
      19,961,984 
Georgia — 3.9%       
County of Fulton Georgia, RB (NPFGC),     
5.25%, 1/01/35    1,000  1,071,350 
Metropolitan Atlanta Rapid Transit       
Authority, RB, Third Series, 5.00%,       
7/01/39    165  176,982 
Municipal Electric Authority of Georgia,     
Refunding RB, Project One,       
Sub-Series D, 6.00%, 1/01/23    5,600  6,477,464 
      7,725,796 

 

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.  HFA  Housing Finance Agency 
AGM  Assured Guaranty Municipal Corp.  HRB  Housing Revenue Bonds 
AMBAC  American Municipal Bond Assurance Corp.  IDA  Industrial Development Authority 
AMT  Alternative Minimum Tax (subject to)  IDRB  Industrial Development Revenue Bonds 
COP  Certificates of Participation  ISD  Independent School District 
EDA  Economic Development Authority  NPFGC  National Public Finance Guarantee Corp. 
ERB  Education Revenue Bonds  RB  Revenue Bonds 
GO  General Obligation Bonds  S/F  Single-Family 

 

BLACKROCK MUNIYIELD INVESTMENT FUND

OCTOBER 31, 2010

1


Schedule of Investments(continued)

BlackRock MuniYield Investment Fund (MYF)
(Percentages shown are based on Net Assets)

    Par   
Municipal Bonds    (000)  Value 
Illinois — 7.3%       
County of Cook Illinois, GO, Refunding,     
Series A, 5.25%, 11/15/33  $ 3,345  $ 3,576,574 
Illinois Finance Authority, Refunding RB:     
Central DuPage Health, Series B,     
5.38%, 11/01/39    1,200  1,263,420 
Northwestern Memorial Hospital,     
Series A, 6.00%, 8/15/39    4,160  4,634,323 
OSF Healthcare System, Series A,     
6.00%, 5/15/39    1,975  2,083,507 
State of Illinois, RB, Build Illinois,       
Series B, 5.25%, 6/15/34    2,700  2,825,631 
      14,383,455 
Indiana — 4.0%       
Indiana Finance Authority, Refunding     
RB, Trinity Health, Series B, 4.50%,     
12/01/37    3,000  2,868,630 
Indiana Municipal Power Agency, RB,     
Series B, 6.00%, 1/01/39    4,525  4,974,785 
      7,843,415 
Kansas — 1.8%       
Kansas Development Finance Authority,     
Refunding RB, Adventist Health,       
5.50%, 11/15/29    3,250  3,567,720 
Kentucky — 4.1%       
Kentucky Economic Development       
Finance Authority, Refunding RB,       
Owensboro Medical Health System,     
Series A, 6.38%, 6/01/40    1,300  1,377,844 
Louisville & Jefferson County       
Metropolitan Government Parking       
Authority, RB, Series A, 5.75%,       
12/01/34    3,200  3,566,304 
Louisville/Jefferson County Metropolitan     
Government, Refunding RB, Jewish     
Hospital & St. Mary's HealthCare,       
6.13%, 2/01/37    2,955  3,143,854 
      8,088,002 
Massachusetts — 2.9%       
Massachusetts HFA, HRB, Series B,       
AMT, 5.50%, 6/01/41    2,535  2,580,224 
Massachusetts HFA, Refunding HRB,     
Series F, AMT, 5.70%, 6/01/40    2,100  2,167,116 
Massachusetts State College Building     
Authority, RB, Series A, 5.50%,       
5/01/39    1,000  1,095,920 
      5,843,260 
Michigan — 3.9%       
Kalamazoo Hospital Finance Authority,     
Refunding RB, Bronson Methodist       
Hospital, 5.50%, 5/15/36    3,945  4,042,008 
Michigan State Building Authority,       
Refunding RB, Facilities Program,       
Series I, 6.00%, 10/15/38    1,250  1,374,275 
Royal Oak Hospital Finance Authority     
Michigan, Refunding RB, William       
Beaumont Hospital, 8.25%, 9/01/39  1,970  2,368,058 
      7,784,341 

 

    Par   
Municipal Bonds    (000)  Value 
Nebraska — 0.3%       
Lancaster County Hospital Authority       
No. 1, RB, Immanuel Obligation       
Group, 5.63%, 1/01/40  $ 625  $ 643,213 
Nevada — 7.6%       
City of Las Vegas Nevada, GO, Limited     
Tax, Performing Arts Center, 6.00%,     
4/01/34    2,850  3,187,070 
County of Clark Nevada, GO, Refunding,     
Transportation, Series A, 5.00%,       
12/01/29    3,600  3,889,044 
County of Clark Nevada, RB:       
Motor Vehicle Fuel Tax, 5.00%,       
7/01/28    1,300  1,373,892 
Series B, 5.75%, 7/01/42    6,055  6,505,189 
      14,955,195 
New Jersey — 3.3%       
New Jersey EDA, Refunding RB, New       
Jersey American Water Co., Inc.       
Project, Series A, AMT, 5.70%,       
10/01/39    2,250  2,356,538 
New Jersey Transportation Trust Fund     
Authority, RB, Transportation System,     
Series A, 5.88%, 12/15/38    2,670  2,971,229 
Tobacco Settlement Financing Corp.       
New Jersey, Refunding RB, Series 1A,     
4.50%, 6/01/23    1,225  1,146,453 
      6,474,220 
New York — 3.8%       
City of Troy New York, Refunding RB,       
Rensselaer Polytechnic, Series A,       
5.13%, 9/01/40    115  118,990 
New York City Transitional Finance       
Authority, RB, Fiscal 2009, Series S-3,     
5.25%, 1/15/39    2,500  2,705,825 
New York Liberty Development Corp.,     
Refunding RB, Second Priority, Bank     
of America Tower at One Bryant Park     
Project, 6.38%, 7/15/49    1,200  1,285,716 
Triborough Bridge & Tunnel Authority,     
RB, General, Series A-2, 5.38%,       
11/15/38    3,030  3,333,788 
      7,444,319 
North Carolina — 5.5%       
North Carolina Capital Facilities Finance     
Agency, RB, Duke Energy Carolinas,     
Series B, 4.38%, 10/01/31    4,475  4,387,648 
North Carolina Medical Care       
Commission, RB, Series A:       
Duke University Health System,       
5.00%, 6/01/42    1,270  1,322,121 
Novant Health Obligation, 4.75%,     
11/01/43 (b)    5,420  5,210,517 
      10,920,286 
Pennsylvania — 3.6%       
Pennsylvania Economic Development     
Financing Authority, RB, American       
Water Co. Project, 6.20%, 4/01/39  1,075  1,182,898 

 

2 BLACKROCK MUNIYIELD INVESTMENT FUND

OCTOBER 31, 2010


Schedule of Investments(continued)

BlackRock MuniYield Investment Fund (MYF)
(Percentages shown are based on Net Assets)

    Par   
Municipal Bonds    (000)  Value 
Pennsylvania (concluded)       
Pennsylvania Turnpike Commission, RB,     
Sub-Series B, 5.25%, 6/01/39  $ 5,650  $ 5,873,740 
      7,056,638 
Texas — 7.7%       
City of Houston Texas, RB, Senior Lien,     
Series A, 5.50%, 7/01/39    1,170  1,264,431 
Conroe ISD Texas, GO, School Building,     
Series A, 5.75%, 2/15/35    1,800  1,973,610 
Harris County Health Facilities       
Development Corp., Refunding RB,     
Memorial Hermann Healthcare       
System, Series B, 7.25%, 12/01/35  800  918,504 
Lower Colorado River Authority, RB,       
5.75%, 5/15/28    1,620  1,739,491 
North Texas Tollway Authority, RB,       
System, First Tier, Series K-1 (AGC),     
5.75%, 1/01/38    1,250  1,383,687 
Tarrant County Cultural Education       
Facilities Finance Corp., RB, Scott &     
White Healthcare, 6.00%, 8/15/45  3,795  4,052,377 
Texas Private Activity Bond Surface       
Transportation Corp., RB, Senior Lien,     
NTE Mobility Partners LLC, North       
Tarrant Express Managed Lanes       
Project, 6.88%, 12/31/39    3,600  3,906,504 
      15,238,604 
Utah — 1.2%       
City of Riverton Utah, RB, IHC Health       
Services Inc., 5.00%, 8/15/41    2,370  2,463,852 
Virginia — 1.0%       
Virginia Public School Authority, RB,       
School Financing, 6.50%, 12/01/35  1,700  1,984,767 
West Virginia — 1.1%       
West Virginia EDA, Refunding RB,       
Appalachian Power Co., Amos Project,     
Series A, 5.38%, 12/01/38 (a)    2,165  2,199,445 
Wyoming — 1.3%       
County of Sweetwater Wyoming,       
Refunding RB, Idaho Power Co.       
Project, 5.25%, 7/15/26    2,430  2,625,445 
Total Municipal Bonds – 95.7%      189,228,600 
Municipal Bonds Transferred to Tender     
Option Bond Trusts (c)       
California — 21.0%       
Bay Area Toll Authority, Refunding RB,     
San Francisco Bay Area, Series F-1,     
5.63%, 4/01/44    2,680  2,975,036 
California Educational Facilities       
Authority, RB, University of Southern     
California, Series A, 5.25%, 10/01/39  4,200  4,547,382 
Grossmont Union High School District,     
GO, Election of 2008, Series B,       
5.00%, 8/01/40    6,000  6,134,400 
Los Angeles Community College District     
California, GO, Election of 2008:       
Series A, 6.00%, 8/01/33    7,697  8,835,877 

 

Municipal Bonds Transferred to Tender  Par   
Option Bond Trusts (c)    (000)  Value 
California (concluded)       
Los Angeles Community College District     
California, GO, Election of 2008       
(concluded):       
Series C, 5.25%, 8/01/39  $ 5,250  $ 5,647,950 
Los Angeles Unified School District       
California, GO, Series I, 5.00%,       
1/01/34    790  819,783 
San Diego Public Facilities Financing       
Authority, Refunding RB, Series B,       
5.50%, 8/01/39    8,412  9,167,360 
University of California, RB, Series O,       
5.75%, 5/15/34    3,000  3,421,020 
      41,548,808 
Colorado — 1.2%       
Colorado Health Facilities Authority,       
Refunding RB, Catholic Healthcare,     
Series A, 5.50%, 7/01/34    2,149  2,315,044 
District of Columbia — 3.6%       
District of Columbia, RB, Series A,       
5.50%, 12/01/30    2,805  3,212,566 
District of Columbia Water & Sewer       
Authority, RB, Series A, 5.50%,       
10/01/39    3,507  3,824,517 
      7,037,083 
Florida — 4.8%       
City of Jacksonville Florida, RB, Better     
Jacksonville (NPFGC), 5.00%,       
10/01/27    2,700  2,775,195 
Hillsborough County Aviation Authority,     
RB, Series A, AMT (AGC), 5.50%,       
10/01/38    3,869  3,990,167 
Lee County Housing Finance Authority,     
RB, Multi-County Program, Series A-2,     
AMT (Ginnie Mae), 6.00%, 9/01/40  1,620  1,822,063 
Manatee County Housing Finance       
Authority, RB, Series A, AMT (Ginnie     
Mae), 5.90%, 9/01/40    911  984,370 
      9,571,795 
Illinois — 4.1%       
Illinois Finance Authority, RB, University     
of Chicago, Series B, 6.25%, 7/01/38  5,300  6,202,961 
Illinois State Toll Highway Authority, RB,     
Series B, 5.50%, 1/01/33    1,750  1,891,464 
      8,094,425 
Nevada — 6.1%       
Clark County Water Reclamation       
District, GO:       
Limited Tax, 6.00%, 7/01/38    5,000  5,647,700 
Series B, 5.50%, 7/01/29    5,668  6,338,801 
      11,986,501 
New Hampshire — 1.2%       
New Hampshire Health & Education       
Facilities Authority, Refunding RB,       
Dartmouth College, 5.25%, 6/01/39  2,159  2,373,235 
New Jersey — 3.4%       
New Jersey State Housing & Mortgage     
Finance Agency, RB, S/F Housing,       
Series CC, 5.25%, 10/01/29    2,291  2,419,708 

 

BLACKROCK MUNIYIELD INVESTMENT FUND

OCTOBER 31, 2010

3


Schedule of Investments(continued)

BlackRock MuniYield Investment Fund (MYF)
(Percentages shown are based on Net Assets)

Municipal Bonds Transferred to Tender  Par   
Option Bond Trusts (c)    (000)  Value 
New Jersey (concluded)       
New Jersey Transportation Trust Fund     
Authority, RB, Transportation System,     
Series A (AGM), 5.00%, 12/15/32  $ 4,000  $ 4,212,800 
      6,632,508 
New York — 4.6%       
New York City Municipal Water Finance     
Authority, RB, Series FF-2, 5.50%,       
6/15/40    2,504  2,826,749 
New York State Dormitory Authority,       
ERB, Series B, 5.25%, 3/15/38    5,700  6,252,045 
      9,078,794 
Ohio — 1.6%       
County of Allen Ohio, Refunding RB,       
Catholic Healthcare, Series A, 5.25%,     
6/01/38    3,120  3,268,294 
South Carolina — 1.8%       
South Carolina State Public Service       
Authority, RB, Santee Cooper,       
Series A, 5.50%, 1/01/38    3,240  3,597,210 
Texas — 5.1%       
City of San Antonio Texas, Refunding     
RB, Series A, 5.25%, 2/01/31    3,989  4,413,389 
Harris County Cultural Education       
Facilities Finance Corp., RB, Hospital,     
Texas Children’s Hospital Project,       
5.50%, 10/01/39    5,400  5,739,984 
      10,153,373 
Virginia — 1.0%       
Fairfax County IDA Virginia, Refunding     
RB, Health Care, Inova Health System,     
Series A, 5.50%, 5/15/35    1,749  1,904,089 
Wisconsin — 1.7%       
Wisconsin Health & Educational       
Facilities Authority, Refunding RB,       
Froedtert & Community Health Inc.,     
5.25%, 4/01/39    3,289  3,460,516 
Total Municipal Bonds Transferred to     
Tender Option Bond Trusts – 61.2%      121,021,675 
Total Long-Term Investments       
(Cost – $291,936,264) – 156.9%      310,250,275 

 

Short-Term Securities  Shares  Value 
FFI Institutional Tax-Exempt Fund,     
0.13% (d)(e)  1,883,610  $ 1,883,610 
Total Short-Term Securities     
(Cost – $1,883,610) – 0.9%    1,883,610 
Total Investments     
(Cost – $293,819,874*) – 157.8%    312,133,885 
Other Assets Less Liabilities – 3.8%    7,422,957 
Liability for Trust Certificates, Including Interest   
Expense and Fees Payable – (31.5)%    (62,262,725) 
Preferred Shares, at Redemption Value – (30.1)%  (59,480,650) 
Net Assets Applicable to Common Shares – 100.0%  $ 197,813,467 

 

* The cost and unrealized appreciation (depreciation) of investments as of

October 31, 2010, as computed for federal income tax purposes, were as
follows: 

Aggregate cost $ 232,352,234 
Gross unrealized appreciation  $ 18,866,891 
Gross unrealized depreciation  $ (1,304,796) 
Net unrealized appreciation   17,562,095 

 

(a) Variable rate security. Rate shown is as of report date.
(b) When-issued security. Unsettled when-issued transactions were as
follows:

    Unrealized 
Counterparty  Value  Appreciation 
JPMorgan Securities  $ 5,210,517  $ 8,455 

 

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

  Shares    Shares   
  Held at    Held at   
  July 31,  Net  October 31,   
Affiliate  2010  Activity  2010  Income 
FFI Institutional         
Tax-Exempt Fund  7,411,011 (5,527,401)    1,883,610 $2,084 
(e) Represents the current yield as of report date.   

 

4 BLACKROCK MUNIYIELD INVESTMENT FUND

OCTOBER 31, 2010


Schedule of Investments(concluded)

BlackRock MuniYield Investment Fund (MYF)

•Fair Value Measurements - Various inputs are used in determining the fair
value of investments, which are as follows:

•Level 1 — price quotations in active markets/exchanges for identical
assets and liabilities

•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)

•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 methodologies 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 annual report.

The following table summarizes the inputs used as of October 31, 2010 in
determining the fair valuation of the Fund's investments:

Valuation Inputs  Level 1  Level 2  Level 3  Total 
Assets:         
Investments in         
Securities:         
Long-Term         
Investments1  -- $ 310,250,275  --  $ 310,250,275 
Short-Term         
Securities  $ 1,883,610  --  --  1,883,610 
Total  $ 1,883,610   $ 310,250,275  --  $ 312,133,885 

 

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

BLACKROCK MUNIYIELD INVESTMENT FUND

OCTOBER 31, 2010

5


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
31940 Act3)) areeffective 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 13a-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 22, 2010

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 22, 2010

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

Date: December 22, 2010