Exhibit 5.1

                      (Stewart McKelvey Stirling Scales)

                                             August 4, 2000

GSI Lumonics Inc.
105 Schneider Road
Kanata, Ontario
Canada K2K 1Y3

Ladies and Gentlemen:

          We have acted as New Brunswick counsel for GSI Lumonics Inc., a New
Brunswick corporation (the "Company"), in connection with the Company's
Registration Statement on Form S-8 proposed to be filed with the Securities and
Exchange Commission on or about August 4, 2000 (the "Registration Statement").

          The Registration Statement covers the registration of up to an
additional 2,000,000 shares of common stock of the Company (the "Shares"), which
are to be issued by the Company upon exercise of stock options granted pursuant
to the 1995 Stock Option Plan for Employees and Directors (the "Plan").

          We have reviewed the corporate proceedings of the Company with respect
to the authorization of the Plan and the issuance of the Shares thereunder and,
in particular, a resolution of the board of directors dated February 4, 2000.
We have also examined and relied upon originals or copies of such agreements,
instruments, corporate records, certificates and other documents as we have
deemed necessary or appropriate as a basis for the opinions hereinafter
expressed.  In our examination, we have assumed the genuineness of all
signatures, the conformity to the originals of all documents reviewed by us as
copies, the authenticity and completeness of all original documents reviewed by
us in original or copy form and the legal competence of each individual
executing any document.

          We further assume that all Shares issued upon exercise of options
granted or to be granted pursuant to the Plan will be issued in accordance with
the terms of such options and the Plan.

          Subject to the limitations set forth below, we have made such
examination of law as we have deemed necessary for the purposes of this opinion.
This opinion is limited solely to New Brunswick law.

          Based upon and subject to the foregoing, we are of the opinion that
the Shares, when issued and delivered upon the exercise of options duly granted
pursuant to the Plan and against the payment of the purchase price or exercise
price therefor as provided in the Plan and


the instrument evidencing the relevant grant, will be duly authorized, validly
issued, fully paid and nonassessable.

          We hereby consent to the filing of this opinion as an exhibit to the
registration statement on Form S-8 by the Company to effect registration of the
Shares issued and sold pursuant to the Plan under the Securities Act of 1933, as
amended.

                              Yours very truly,

                              STEWART McKELVEY STIRLING SCALES