N-CSR Item 12(b) - Exhibits: Certifications

                           SECTION 906 CERTIFICATION

Pursuant to 18 U.S.C.{section} 1350, the undersigned officers of FEDERATED
MUNICIPAL SECURITIES INCOME TRUST on behalf of Federated Pennsylvania Municipal
Income Fund (the "Registrant"), hereby certify, to the best of our knowledge,
that the Registrant's Report on Form N-CSR for the period ended August 31, 2006
(the "Report") fully complies with the requirements of Section 13(a) or 15(d),
as applicable, of the Securities and Exchange Act of 1934 and that the
information contained in the Report fairly presents, in all material respects,
the financial condition and results of operations of the Registrant.


Dated: January 9, 2007

/s/ J. Christopher Donahue
Name: J. Christopher Donahue
Title: President, Principal Executive Officer



Dated: January 9, 2007

/s/ Richard A. Novak
Name: Richard A. Novak
Title: Treasurer, Principal Financial Officer

This certification is being furnished solely pursuant to 18 U.S.C.{section} 1350
and is not being filed as part of the Report or as a separate disclosure
document.