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


         The undersigned, the Chief Executive Officer of the SEI Institutional
Investments Trust (the "Fund"), with respect to the Fund's Form N-CSRS for the
period ended November 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-CSRS 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-CSRS fairly presents, in
all material respects, the financial condition and results of operations of the
Fund.


Dated: January 29, 2009



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

                                                  Chief Executive Officer