EXHIBIT 99.3


                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

        In connection with the Annual Report of GSI LUMONICS INC. (the
"Company") on Form 10-K for the period ending December 31, 2002 as filed with
the Securities and Exchange Commission on the date hereof (the "Report"), I,
Thomas R. Swain, Chief Financial Officer of the Company, certify, 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) 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 result of operations of the
Company.




/s/ Thomas R. Swain
- --------------------
Thomas R. Swain
Chief Financial Officer
March 28, 2003



This Certification shall not be deemed part of the Report or incorporated by
reference into any of the Company's filings with the Securities and Exchange
Commission by implication or by any reference in any such filings to the Report.