CERTIFICATION
                             Pursuant to Section 906
                        of the Sarbanes-Oxley Act of 2002


         The undersigned, the Chief Executive Officer of SEI Institutional
Managed Trust (the "Fund"), with respect to the Fund's Form N-CSR for the year
ended September 30, 2008 as filed with the Securities and Exchange Commission,
hereby certifies, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to
Section 906 of the Sarbanes-Oxley Act of 2002, that, to the best of my
knowledge:

         1. such Form N-CSR fully complies with the requirements of section
13(a) or 15(d) of the Securities Exchange Act of 1934; and

         2. the information contained in such Form N-CSR fairly presents, in all
material respects, the financial condition and results of operations of the
Fund.


Dated: November 26, 2008


                                       /s/ Robert A. Nesher
                                       --------------------
                                       Robert A. Nesher