EXHIBIT 5.1(a)

                      [LETTERHEAD OF O'MELVENY & MYERS LLP]



                                December 15, 2004



Nissan Auto Receivables Corporation II
Nissan Motor Acceptance Corporation
Nissan Auto Receivables Trusts
990 West 190th Street
Torrance, California 90502

      Re:   Nissan Auto Receivables Corporation II
            Nissan Motor Acceptance Corporation
            Nissan Auto Receivables Trusts
            Registration Statement on Form S-3
            Relating to Asset-Backed Securities

Ladies and Gentlemen:

      We have acted as special counsel to Nissan Auto Receivables Corporation II
("NARC II"), a Delaware corporation and wholly-owned limited purpose subsidiary
of Nissan Motor Acceptance Corporation ("NMAC"), a California corporation, and
certain trusts, all of the beneficial ownership of which will initially be owned
by NARC II (together with NARC II, each an "Issuer"), in connection with the
proposed issuance of $12,430,343,000 aggregate principal amount of asset-backed
notes (the "Notes") to be offered pursuant to a registration statement on Form
S-3 relating to the Notes (such registration statement, as amended, the
"Registration Statement") being filed with the Securities and Exchange
Commission concurrently herewith under the Securities Act of 1933, as amended
(the "1933 Act"), and the rules and regulations promulgated thereunder. The
Notes will be issued under and pursuant to the indenture for each series, each
between the applicable Issuer and the Indenture Trustee (as defined therein).
The indenture in the form filed with the Securities and Exchange Commission on
October 29, 2004, as an exhibit to the Registration Statement, is herein
referred to as the "Indenture."

      We have examined originals or copies, certified or otherwise identified to
our satisfaction, of the organizational documents of the Issuers, the Indenture,
the form of Notes included as an exhibit to the Indenture, and such other
records, documents and certificates of the Issuers and public officials and
other instruments as we have deemed necessary for the purpose of this opinion.
In addition, we have assumed that the Indenture as completed for each series
will be duly executed and delivered by the parties thereto; that the Notes as
completed for each series will be duly executed and delivered substantially in
the forms contemplated by the

Indenture; and that the Notes for each series will be sold as described in the
Registration Statement.

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

      The Notes are in due and proper form and, assuming the due authorization,
execution and delivery of the Indenture by the applicable Issuer and the
Indenture Trustee, and the due authorization of the Notes for each series by all
necessary action on the part of the applicable Issuer, when the Notes for each
series have been validly executed, authenticated and issued in accordance with
the applicable Indenture and delivered against payment therefor, the Notes for
each series will be valid and binding obligations of the applicable Issuer,
enforceable against the applicable Issuer in accordance with their terms,
subject to bankruptcy, insolvency, reorganization, moratorium or other similar
laws relating to or affecting creditors' rights generally (including, without
limitation, fraudulent conveyance laws), and general principles of equity,
including without limitation, concepts of materiality, reasonableness, good
faith and fair dealing and the possible unavailability of specific performance
or injunctive relief, regardless of whether such enforceability is considered in
a proceeding in equity or at law.

      The opinions expressed above are limited to the federal laws of the United
States of America and the laws of the State of New York (excluding choice of law
principles therein). We express no opinion herein as to the laws of any other
jurisdiction and no opinion regarding the statutes, administrative decisions,
rules, regulations or requirements of any county, municipality, subdivision or
local authority of any jurisdiction.

      We consent to the filing of this letter as an exhibit to the Registration
Statement and to the reference to this firm under the heading "Legal Opinions"
in the Prospectus and the Prospectus Supplement, without admitting that we are
"experts" within the meaning of the 1933 Act or the rules or regulations of the
Securities and Exchange Commission thereunder, with respect to any part of the
Registration Statement, including this exhibit.

                                        Respectfully submitted,

                                        /s/ O'Melveny & Myers LLP