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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: 04/30/2010

Item 1 – Schedule of Investments

Schedule of Investments April 30, 2010 (Unaudited)

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

     Par   
Municipal Bonds    (000)  Value 
Arizona — 0.7%       
Pima County IDA, Refunding IDRB,       
   Tucson Electric Power, 5.75%,       
   9/01/29  $ 1,230  $ 1,251,623 
California — 14.5%       
California Health Facilities Financing       
   Authority, Refunding RB, Series A:       
       Catholic Healthcare West, 6.00%,       
       7/01/39    710  761,113 
       St. Joseph Health System, 5.75%,       
       7/01/39    2,700  2,807,001 
California State Public Works Board, RB:     
       Department of General Services,       
       Buildings 8 & 9, Series A, 6.25%,       
       4/01/34    4,525  4,790,889 
       Various Capital Projects,       
       Sub-Series I-1, 6.38%, 11/01/34    1,265  1,355,258 
Los Angeles Department of Airports,       
   Refunding RB, Senior, Los Angeles       
   International Airport, Series A, 5.00%,     
   5/15/35    5,420  5,553,223 
Los Angeles Department of Water &       
   Power, RB, Power System,       
   Sub-Series A-1, 5.25%, 7/01/38    3,300  3,534,960 
San Diego Regional Building Authority       
   California, RB, County Operations       
   Center & Annex, Series A, 5.38%,       
   2/01/36    3,310  3,497,776 
San Francisco City & County Airports       
   Commission, Refunding RB, Second       
   Series A-3, AMT, 6.75%, 5/01/19    2,500  2,611,950 
State of California, GO, Various Purpose,     
   6.00%, 3/01/33    2,535  2,790,300 
      27,702,470 
Colorado — 2.2%       
City & County of Denver Colorado,       
   Refunding RB, Series A, 5.25%,       
   11/15/36    4,050  4,191,264 
District of Columbia — 1.1%       
District of Columbia Water & Sewer       
   Authority, RB, Series A, 5.25%,       
   10/01/29    2,000  2,138,780 

  Par   
Municipal Bonds  (000)  Value 
Florida — 19.2%     
Broward County Educational Facilities     
   Authority, RB, Nova Southeastern     
   University (AGC), 5.00%, 4/01/31  $ 1,810  $ 1,828,390 
City of Jacksonville Florida, RB, Series B     
   (NPFGC), 5.13%, 10/01/32  1,500  1,515,045 
City of Jacksonville Florida, Refunding     
   RB (NPFGC), 5.25%, 10/01/32  2,315  2,346,345 
City of Port St. Lucie Florida, RB     
   (NPFGC), 5.25%, 9/01/25  1,215  1,238,000 
County of Miami-Dade Florida, RB, AMT,     
   Series A:     
       (AGM), 5.00%, 10/01/33  505  486,759 
       Miami International Airport, (AGM),     
       5.25%, 10/01/41  515  508,727 
       Miami International Airport, (AGM),     
       5.50%, 10/01/41  2,930  2,963,285 
       Miami International Airport,     
       (NPFGC), 6.00%, 10/01/29  3,275  3,315,675 
County of Orange Florida, Refunding RB     
   (AMBAC), 5.00%, 10/01/29  1,750  1,787,380 
County of Osceola Florida, RB, Series A     
   (NPFGC), 5.50%, 10/01/27  1,760  1,797,822 
County of Sumter Florida, RB (AMBAC),     
   5.00%, 6/01/26  1,000  1,013,040 
Florida Housing Finance Corp.,     
   Refunding RB, Homeowner Mortgage,     
   Series 4, AMT (AGM), 6.25%,     
   7/01/22  345  358,631 
Florida Municipal Loan Council, RB,     
   Series A-1 (NPFGC), 5.13%, 7/01/34  1,580  1,584,298 
Hillsborough County IDA, RB, AMT,     
   National Gypsum Co:     
       Series A, 7.13%, 4/01/30  2,500  2,177,525 
       Series B, 7.13%, 4/01/30  3,750  3,266,287 
Lee County Housing Finance Authority,     
   RB, Multi-County Program, Series A-1,     
   AMT (GNMA), 7.13%, 3/01/28  25  25,378 
Manatee County Housing Finance     
   Authority, Refunding RB, S/F, Sub-     
   Series 1, AMT (GNMA), 6.25%,     
   11/01/28  85  89,262 

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 
CIFG  CDC IXIS Financial Guaranty  ISD  Independent School District 
COP  Certificates of Participation  NPFGC  National Public Finance Guarantee Corp. 
DRIVERS  Derivative Inverse Tax-Exempt Receipts  PUTTERS  Puttable Tax-Exempt Receipts 
EDA  Economic Development Authority  RB  Revenue Bonds 
ERB  Education Revenue Bonds  S/F  Single-Family 
GNMA  Government National Mortgage Association     
GO  General Obligation Bonds     

BLACKROCK MUNIYIELD INVESTMENT FUND

APRIL 30, 2010

1

Schedule of Investments (continued)

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

     Par   
Municipal Bonds    (000)  Value 
Florida (concluded)       
Miami-Dade County Housing Finance       
   Authority Florida, Refunding RB, Home     
   Ownership Mortgage, Series A1, AMT     
   (GNMA), 6.30%, 10/01/20  $ 365  $ 372,388 
Polk County School Board, COP, Master     
   Lease, Series A (AGM), 5.50%,       
   1/01/25    4,385  4,499,887 
Santa Rosa County School Board, COP,     
   Refunding, Series 2 (NPFGC), 5.25%,     
   2/01/26    1,180  1,235,295 
South Lake County Hospital District, RB,     
   South Lake Hospital Inc., 6.38%,       
   10/01/34    1,150  1,156,394 
Village Center Community Development     
   District, RB, Series A (NPFGC):       
       5.38%, 11/01/34    1,995  1,782,094 
       5.13%, 11/01/36    1,000  857,520 
Volusia County IDA, RB, Student       
   Housing, Stetson University Project,       
   Series A (CIFG), 5.00%, 6/01/35    500  427,500 
      36,632,927 
Georgia — 8.2%       
City of Atlanta Georgia, RB, General,       
   Subordinate Lien, Series C (AGM),       
   5.00%, 1/01/33    3,270  3,301,621 
County of Fulton Georgia, RB (NPFGC),     
   5.25%, 1/01/35    1,000  1,039,480 
Metropolitan Atlanta Rapid Transit       
   Authority, RB, Third Series, 5.00%,       
   7/01/39    4,815  5,067,884 
Municipal Electric Authority of Georgia,     
   Refunding RB, Project One,       
   Sub-Series D, 6.00%, 1/01/23    5,600  6,352,752 
      15,761,737 
Illinois — 4.5%       
Illinois Finance Authority, Refunding RB:     
       Central DuPage Health, Series B,       
       5.38%, 11/01/39    1,200  1,235,544 
       Northwestern Memorial Hospital,       
       Series A, 6.00%, 8/15/39    4,160  4,536,854 
State of Illinois, RB, Build Illinois,       
   Series B, 5.25%, 6/15/34    2,700  2,813,076 
      8,585,474 
Indiana — 2.6%       
Indiana Municipal Power Agency, RB,       
   Indiana Municipal Power Agency,       
   Series B, 6.00%, 1/01/39    4,525  4,889,398 
Kansas — 1.8%       
Kansas Development Finance Authority,     
   Refunding RB, Adventist Health,       
   5.50%, 11/15/29    3,250  3,435,185 

     Par   
Municipal Bonds    (000)  Value 
Kentucky — 4.1%       
Kentucky Economic Development       
   Finance Authority, Refunding RB,       
   Owensboro Medical Health System,       
   Series A, 6.38%, 6/01/40  $ 1,300  $ 1,336,400 
Louisville & Jefferson County       
   Metropolitan Government Parking       
   Authority, RB, Series A, 5.75%,       
   12/01/34    3,200  3,516,384 
Louisville/Jefferson County Metropolitan     
   Government, Refunding RB, Jewish       
   Hospital & St. Mary's HealthCare,       
   6.13%, 2/01/37    2,955  3,068,117 
      7,920,901 
Massachusetts — 2.4%       
Massachusetts HFA, Refunding HRB,       
   Series F, AMT, 5.70%, 6/01/40    2,110  2,142,789 
Massachusetts Health & Educational       
   Facilities Authority, RB, Tufts       
   University, 5.38%, 8/15/38    1,250  1,356,425 
Massachusetts State College Building     
   Authority, RB, Series A, 5.50%,       
   5/01/39    1,000  1,081,820 
      4,581,034 
Michigan — 2.1%       
Michigan State Building Authority,       
   Refunding RB, Facilities Program,       
   Series I, 6.00%, 10/15/38    1,250  1,354,150 
Michigan State Hospital Finance       
   Authority, Refunding RB, Hospital,       
   Henry Ford Health, 5.75%, 11/15/39  410  404,256 
Royal Oak Hospital Finance Authority       
   Michigan, Refunding RB, William       
   Beaumont Hospital, 8.25%, 9/01/39  1,970  2,325,250 
      4,083,656 
Nebraska — 0.3%       
Lancaster County Hospital Authority       
   No. 1, RB, Immanuel Obligation       
   Group, 5.63%, 1/01/40    625  626,563 
Nevada — 9.9%       
City of Las Vegas Nevada, GO, Limited     
   Tax, Performing Arts Center, 6.00%,     
   4/01/34    2,850  3,147,882 
County of Clark Nevada, GO, Refunding,     
   Transportation, Series A, 5.00%,       
   12/01/29    4,800  4,977,456 
County of Clark Nevada, RB:       
Motor Vehicle Fuel Tax, 5.00%,       
7/01/28    4,300  4,427,237 
Series B, 5.75%, 7/01/42    6,055  6,413,638 
      18,966,213 

2 BLACKROCK MUNIYIELD INVESTMENT FUND

APRIL 30, 2010

Schedule of Investments (continued)

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

  Par   
Municipal Bonds  (000)  Value 
New Jersey — 3.4%     
New Jersey EDA, Refunding RB, New     
   Jersey American Water Co., Series A,     
   AMT, 5.70%, 10/01/39  $ 2,250  $ 2,297,880 
New Jersey Transportation Trust Fund     
   Authority, RB, Transportation System,     
   Series A, 5.88%, 12/15/38  2,670  2,929,871 
Tobacco Settlement Financing Corp.     
   New Jersey, Refunding RB, Series 1A,     
   4.50%, 6/01/23  1,290  1,232,131 
    6,459,882 
New York — 8.1%     
City of Troy New York, Refunding RB,     
   Rensselaer Polytechnic, Series A,     
   5.13%, 9/01/40  3,260  3,329,340 
New York City Transitional Finance     
   Authority, RB, Fiscal 2009, Series S-3,     
   5.25%, 1/15/39  2,500  2,654,050 
New York State Dormitory Authority,     
   ERB, Series B, 5.25%, 3/15/38  5,700  6,156,855 
Triborough Bridge & Tunnel Authority,     
   RB, General, Series A-2, 5.38%,     
   11/15/38  3,030  3,292,338 
    15,432,583 
North Carolina — 1.3%     
City of Charlotte North Carolina,     
   Refunding RB, Series A, 5.50%,     
   7/01/34  350  372,113 
North Carolina Eastern Municipal Power     
   Agency, Refunding RB, Series B,     
   5.00%, 1/01/26  885  918,356 
North Carolina Medical Care     
   Commission, RB, Duke University     
   Health System, Series A, 5.00%,     
   6/01/42  1,270  1,289,405 
    2,579,874 
Pennsylvania — 3.7%     
Pennsylvania Economic Development     
   Financing Authority, RB, American     
   Water Co. Project, 6.20%, 4/01/39  1,075  1,162,043 
Pennsylvania Turnpike Commission, RB,     
   Sub-Series B, 5.25%, 6/01/39  5,650  5,839,388 
    7,001,431 
Puerto Rico — 0.5%     
Puerto Rico Housing Finance Authority,     
   Refunding RB, Subordinate, Capital     
   Fund Modernization, 5.13%,     
   12/01/27  920  918,372 
Texas — 7.7%     
City of Houston Texas, RB, Senior Lien,     
   Series A, 5.50%, 7/01/39  1,170  1,246,694 
Conroe ISD Texas, GO, School Building,     
   Series A, 5.75%, 2/15/35  1,800  1,951,290 

     Par   
Municipal Bonds    (000)  Value 
Texas (concluded)       
Harris County Health Facilities       
   Development Corp., Refunding RB,       
   Memorial Hermann Healthcare       
   System, B, 7.25%, 12/01/35  $ 800  $ 901,736 
Lower Colorado River Authority, RB,       
   5.75%, 5/15/28    1,620  1,722,400 
North Texas Tollway Authority, RB,       
   System, First Tier, Series K-1 (AGC),       
   5.75%, 1/01/38    1,750  1,893,728 
Tarrant County Cultural Education       
   Facilities Finance Corp., RB,       
   Ascension Health Senior Credit Group,     
   5.00%, 11/15/29    3,250  3,331,737 
Texas Private Activity Bond Surface       
   Transportation Corp., RB, Senior Lien,     
   Note Mobility, 6.88%, 12/31/39    3,600  3,760,992 
      14,808,577 
Utah — 1.3%       
City of Riverton Utah, RB, IHC Health       
   Services Inc., 5.00%, 8/15/41    2,370  2,410,361 
Virginia — 1.0%       
Virginia Public School Authority, RB,       
   School Financing, 6.50%, 12/01/35  1,700  1,964,741 
Wyoming — 1.3%       
County of Sweetwater Wyoming,       
   Refunding RB, Idaho Power Co.       
   Project, 5.25%, 7/15/26    2,430  2,569,093 
 Total Municipal Bonds – 101.9%                                           194,912,139
Municipal Bonds Transferred to Tender     
Option Bond Trusts (a)       
California — 15.3%       
Bay Area Toll Authority, Refunding RB,     
   San Francisco Bay Area, Series F-1,       
   5.63%, 4/01/44    2,680  2,918,354 
California Educational Facilities       
   Authority, RB, University of Southern     
   California, Series A, 5.25%, 10/01/18  4,200  4,503,744 
Los Angeles Community College District     
   California, GO, Election of 2008,       
   Series A, 6.00%, 8/01/33    7,697  8,630,287 
Los Angeles Unified School District       
   California, GO, Series I, 5.00%,       
   1/01/34    790  803,904 
San Diego Public Facilities Financing       
   Authority, Refunding RB, Series B,       
   5.50%, 8/01/39    8,412  9,029,606 
University of California, RB, Series O,       
   5.75%, 5/15/34    3,000  3,368,370 
      29,254,265 

BLACKROCK MUNIYIELD INVESTMENT FUND

APRIL 30, 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 (a)    (000)  Value 
Colorado — 1.2%       
Colorado Health Facilities Authority,       
   Refunding RB, Catholic Healthcare,       
   Series A, 5.50%, 7/01/34  $ 2,149  $ 2,279,504 
District of Columbia — 3.6%       
District of Columbia, RB, Series A,       
   5.50%, 12/01/30     2,805  3,149,061 
District of Columbia Water & Sewer       
   Authority, RB, Series A, 5.50%,       
   10/01/39     3,507  3,786,820 
      6,935,881 
Florida — 10.0%       
City of Jacksonville Florida, RB, Better       
   Jacksonville (NPFGC), 5.00%,       
   10/01/27     2,700  2,766,312 
Hillsborough County Aviation Authority,     
   RB, Series A, AMT (AGC), 5.50%,       
   10/01/38     3,869  3,918,108 
Lee County Housing Finance Authority,     
   RB, Multi-County Program, Series A-2,     
   AMT (GNMA), 6.00%, 9/01/40     1,830  1,981,597 
Manatee County Housing Finance       
   Authority, RB, Series A, AMT (GNMA),     
   5.90%, 9/01/40     1,131  1,176,766 
South Broward Hospital District, RB,       
   Hospital (NPFGC), 5.63%, 5/01/32 (b)   8,500  9,351,955 
      19,194,738 
Illinois — 4.2%       
Illinois Finance Authority, RB, University     
   of Chicago, Series B, 6.25%, 7/01/38   5,300  6,119,751 
Illinois State Toll Highway Authority, RB,     
   Series B, 5.50%, 1/01/33     1,750  1,901,019 
      8,020,770 
Nevada — 6.2%       
Clark County Water Reclamation       
   District, GO:       
Limited Tax, 6.00%, 7/01/38     5,000  5,598,250 
Series B, 5.50%, 7/01/29     5,668  6,219,504 
      11,817,754 
New Hampshire — 1.2%       
New Hampshire Health & Education       
   Facilities Authority, Refunding RB,       
   Dartmouth College, 5.25%, 6/01/39   2,159  2,343,989 
New Jersey — 1.2%       
New Jersey State Housing & Mortgage     
   Finance Agency, RB, S/F Housing,       
   Series CC, 5.25%, 10/01/29     2,291  2,361,267 
New York — 1.5%       
New York City Municipal Water Finance     
   Authority, RB, Series FF-2, 5.50%,       
   6/15/40     2,504  2,785,041 

Municipal Bonds Transferred to Tender           Par   
Option Bond Trusts (a)  (000)  Value 
Ohio — 1.7%     
County of Allen Ohio, JP Morgan Chase     
   PUTTERS/DRIVERS Trust, Refunding     
   RB, Series 3692Z, 9.00%,     
 6/01/38 (c)  $ 3,120  $ 3,203,429 
South Carolina — 1.8%     
South Carolina State Public Service     
   Authority, RB, Santee Cooper,     
   Series A, 5.50%, 1/01/38  3,240  3,528,490 
Texas — 5.2%     
City of San Antonio Texas, Refunding     
   RB, Series A, 5.25%, 2/01/31  3,989  4,347,953 
Harris County Cultural Education     
   Facilities Finance Corp., RB, Hospital,     
   Texas Children's Hospital Project,     
   5.50%, 10/01/39  5,400  5,617,080 
    9,965,033 
Virginia — 1.0%     
Fairfax County IDA Virginia, Refunding     
   RB, Health Care, Inova Health System,     
   Series A, 5.50%, 5/15/35  1,749  1,852,202 
Wisconsin — 1.8%     
Wisconsin Health & Educational     
   Facilities Authority, Refunding RB,     
   Froedtert & Community Health Inc.,     
   5.25%, 4/01/39  3,289  3,369,124 
Total Municipal Bonds Transferred to     
Tender Option Bond Trusts – 55.9%    106,911,487 
Total Long-Term Investments     
 (Cost – $288,215,986) – 157.8%                                           301,823,626
Short-Term Securities  Shares   
FFI Institutional Tax-Exempt Fund,     
   0.25% (d)(e)  3,518,610  3,518,610 
Total Short-Term Securities     
(Cost – $3,518,610) – 1.8%    3,518,610 
Total Investments     
(Cost – $291,734,596*) – 159.6%    305,342,236 
Other Assets Less Liabilities – 0.9%    1,684,104 
Liability for Trust Certificates, Including Interest   
Expense and Fees Payable – (29.4)%    (56,282,189) 
Preferred Shares, at Redemption Value – (31.1)%  (59,481,098) 
Net Assets Applicable to Common Shares – 100.0% $  191,263,053 

4 BLACKROCK MUNIYIELD INVESTMENT FUND

APRIL 30, 2010

Schedule of Investments (concluded)

BlackRock MuniYield Investment Fund (MYF)

* The cost and unrealized appreciation (depreciation) of investments as of
April 30, 2010, as computed for federal income tax purposes, were as
follows:

Aggregate cost  $ 236,711,512 
Gross unrealized appreciation  $ 14,907,404 
Gross unrealized depreciation  (2,521,329) 
Net unrealized appreciation  $ 12,386,075 

(a) 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.
(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) When-issued security. Unsettled when-issued transactions were as
follows:

    Unrealized 
Counterparty  Value  Appreciation 
JP Morgan Securities  $ 1,643,429  $ 28,833 

(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, were as follows:

  Shares    Shares   
  Held at    Held at   
  July 31,  Net  April 30,   
     Affiliate  2009  Activity  2010  Income 
     FFI Institutional         
     Tax-Exempt Fund  1,400,051  2,118,559   3,518,610    $ 9,944 
(e) Represents the current yield as of report date.     

• 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 semi-annual report.

The following table summarizes the inputs used as of April 30, 2010 in
determining the fair valuation of the Fund's investments:

  Investments in Securities     
Valuation Inputs      Level 1  Level 2  Level 3  Total 
Assets:           
Long-Term           
Investments1  --  $ 301,823,626       --   $ 301,823,626 
Short-Term           
Securities  $ 3,518,610         --       --  3,518,610 
Total  $ 3,518,610   $ 301,823,626       --   $ 305,342,236 

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

BLACKROCK MUNIYIELD INVESTMENT FUND

APRIL 30, 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
“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: June 28, 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: June 28, 2010

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

Date: June 28, 2010