Exhibit 99.1350CERT

Certification Pursuant to Rule 30a-2(b) under the 1940 Act and
Section 906 of the Sarbanes-Oxley Act of 2002

Pursuant to 18 U.S.C. § 1350, the undersigned officer of BlackRock MuniYield Investment Fund (the “Registrant”),
hereby certifies, to the best of his knowledge, that the Registrant’s Report on Form N-CSR for the period ended July
31, 2011 (the “Report”) fully complies with the requirements of Section 13(a) of the Securities Exchange Act of
1934, as amended, and that the information contained in the Report fairly presents, in all material respects, the
financial condition and results of operations of the Registrant.

Date: October 4, 2011

/S/ John M. Perlowski
John M. Perlowski
Chief Executive Officer (principal executive officer) of
BlackRock MuniYield Investment Fund

Pursuant to 18 U.S.C. § 1350, the undersigned officer of BlackRock MuniYield Investment Fund (the “Registrant”),
hereby certifies, to the best of his knowledge, that the Registrant’s Report on Form N-CSR for the period ended July
31, 2011 (the “Report”) fully complies with the requirements of Section 13(a) of the Securities Exchange Act of
1934, as amended, and that the information contained in the Report fairly presents, in all material respects, the
financial condition and results of operations of the Registrant.

Date: October 4, 2011

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

This certification is being furnished pursuant to Rule 30a-2(b) under the Investment Company Act of 1940, as
amended, and 18 U.S.C. Section 1350 and is not being filed as part of the Form N-CSR with the Securities and
Exchange Commission.