Exhibit 5.1


                      [MCCARTER & ENGLISH, LLP LETTERHEAD]

                                                              September 12, 2003


One Liberty Properties, Inc.
60 Cutter Mill Road
Great Neck, NY  11021

Ladies and Gentlemen:

      This opinion is furnished in connection with the registration statement on
Form S-3 (the "Registration Statement") pursuant to the Securities Act of 1933,
as amended (the "Securities Act"), relating to an indeterminate amount of shares
of common stock, par value $1.00 per share of One Liberty Properties, Inc., a
Maryland corporation (the "Company"), with an aggregate public offering price of
up to $200,000,000 (the "Securities"). The Registration Statement provides that
the Securities may be offered in amounts, at prices and on terms to be set forth
in one or more prospectus supplements (each a "Prospectus Supplement") to the
Prospectus contained in the Registration Statement.

      We have examined originals, or copies certified or otherwise identified to
our satisfaction, of such documents and corporate and public records as we deem
necessary as a basis for the opinion hereafter expressed. With respect to such
examination, we have assumed the genuineness of all signatures appearing on all
documents presented to us as originals, and the conformity of the originals of
all documents presented to us as conformed or reproduced copies. Where factual
matters relevant to such opinion were not independently established, we have
relied upon certificates of appropriate state and local officials, and upon
certificates of executive officers and responsible employees and agents of the
Company.

One Liberty Properties, Inc.
September 12, 2003
Page 2



      Based upon the foregoing, we are of the opinion that:

      1. The Company is duly incorporated and existing under the laws of the
State of Maryland.

      2. When specifically authorized for issuance by the Company's Board of
Directors or an authorized committee thereof (the "Board Authorization") and
when issued as described in the Registration Statement and a Prospectus
Supplement that is consistent with the Board Authorization, and upon receipt by
the Company of the consideration provided for in the Board Authorization (which
consideration is not less than the $1.00 par value per share), the Securities
covered by the Registration Statement will be legally issued, fully paid and
nonassessable.

      The foregoing assumes that all requisite steps will be taken to comply
with the requirements of the Securities Act and applicable requirements of state
laws regulating the offer and sale of securities.

      We hereby consent to being named as counsel to the Company in the
Registration Statement, to the reference therein to our firm under the caption
"Legal Matters" and to the inclusion of this opinion as an exhibit to the
Registration Statement. In giving this consent, we do not thereby concede that
we come within the categories of persons whose consent is required by the
Securities Act or the General Rules and Regulations promulgated thereunder.

                                                Very truly yours,

                                                /s/ McCarter & English, LLP

                                                McCarter & English, LLP