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

                           SECTION 906 CERTIFICATION

Pursuant to 18 U.S.C.{section} 1350, the undersigned officers of FEDERATED MDT
SERIES on behalf of Federated MDT All Cap Core Fund, Federated MDT Balanced
Fund, Federated MDT Large Cap Growth Fund, Federated Mid Cap Growth Fund,
Federated MDT Small Cap Core Fund, Federated MDT Small Cap Growth Fund,
Federated MDT Small Cap Value Fund, Federated MDT Tax Aware/All Cap Core Fund
(the "Registrant"), hereby certify, to the best of our knowledge, that the
Registrant's Report on Form N-CSR for the period ended July 31, 2007 (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:  September 20, 2007

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



Dated: September 20, 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.