Exhibit 99.906.CERT

CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Certified Shareholder Report of the MML Series Investment
Fund (the "Trust") on From N-CSR for the period ending December 31, 2004, as
filed with the Securities and Exchange Commission on the date hereof ("the
Report"), the undersigned hereby certifies that:

1.   The Report 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 the Report fairly presents, in all material
     respects, the financial condition and results of operations of the Trust.

Date:  2/24/05        /s/ David W. O'Leary
      -----------    -----------------------------------------------------------
                      David W. O'Leary President and Principal Executive Officer


This certification is being furnished to the Commission solely 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
Commission.



CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Certified Shareholder Report of the MML Series Investment
Fund (the "Trust") on From N-CSR for the period ending December 31, 2004, as
filed with the Securities and Exchange Commission on the date hereof ("the
Report"), the undersigned hereby certifies that:

3.   The Report fully complies with the requirements of section 13(a) or 15(d)
     of the Securities Exchange Act of 1934, and

4.   The information contained in the Report fairly presents, in all material
     respects, the financial condition and results of operations of the Trust.

Date:  3/1/05         /s/ James S. Collins
      -----------    -----------------------------------------------------------
                      James S. Collins Treasurer and Principal Financial Officer


This certification is being furnished to the Commission solely 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
Commission.