EXHIBIT 32.1

                            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, 2004 as filed with the Securities
and Exchange Commission on the date hereof (the "Report"), I, Charles D.
Winston, Chief Executive 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/ CHARLES D. WINSTON
                                           -------------------------------------
                                           Charles D. Winston
                                           President and Chief Executive Officer

March 16, 2005

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.

A signed original of this written statement required by Section 906, or other
document authenticating, acknowledging, or otherwise adopting the signature that
appears in typed form with the electronic version of this written statement
required by Section 906, has been provided to GSI Lumonics Inc. and will be
retained by GSI Lumonics Inc. and furnished to the Securities and Exchange
Commission or its staff upon request.