OPINION OF JACKSON WALKER L.L.P.

EXHIBIT 5.1


February 9, 1998

Quanta Services, Inc.
3555 Timmons Lane
Suite 610
Houston, Texas 77027

Re: Registration Statement on Form S-1 of Quanta Services, Inc.
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Ladies and Gentlemen:

We are acting as counsel for Quanta Services, Inc., a Delaware corporation
(the "Company"), in connection with the registration under the Securities Act of
1933, as amended (the "Act"), of the offering and sale of up to 5,000,000 shares
(and up to an additional 750,000 shares to cover Underwriters' overallotments)
of the Company's Common Stock, par value $0.00001 per share (the "Shares"),
which Shares are issuable in connection with the Company's initial public
offering. A Registration Statement (as amended, the "Registration Statement") on
Form S-1 (No. 333-42957) covering the offering and sale of the Shares was filed
with the Securities and Exchange Commission (the "Commission") on December 22,
1997.

In reaching the conclusions expressed in this opinion, we have examined and
relied upon originals or certified copies of all documents, certificates and
instruments as we have deemed necessary to the opinions expressed herein. In
making the foregoing examinations, we have assumed the genuineness of all
signatures on original documents, the authenticity of all documents submitted to
us as originals and the conformity of original documents to all copies submitted
to us.

Based solely upon the foregoing, subject to the comments hereinafter
stated, and limited in all respects to the laws of the State of Texas, the
General Corporation Law of the State of Delaware and the federal laws of the
United States of America, it is our opinion that the Shares, when sold in
accordance with the terms of the Underwriting Agreement, a form of which was
filed as an exhibit to the Registration Statement, will be validly and legally
issued, fully paid and nonassessable.

You should be aware that we are not admitted to practice law in the State
of Delaware. Accordingly, any opinion herein as to the laws of the State of
Delaware is based solely upon the latest generally available compilation of the
statutes and case law of such state.

Quanta Services, Inc.

February 9, 1998
Page 2


We hereby consent to the use of this opinion as an Exhibit to the
Registration Statement and to the reference to us under "Legal Matters" in the
prospectus forming part of the Registration Statement. In giving this consent,
we do not admit that we come within the category of persons whose consent is
required under Section 7 of the Act or the rules and regulations of the
Commission promulgated thereunder.


Very truly yours,

/s/ Jackson Walker L.L.P.

JACKSON WALKER L.L.P.