EXHIBIT 5.1


                     [Letterhead of Pillsbury Winthrop LLP]

September 30, 2003

UnionBanCal Corporation
400 California Street
San Francisco, California 94104

     Re:  Post-Effective  Amendment No. 1 to the Registration  Statement on Form
          S-3 of UnionBanCal Corporation

Ladies and Gentlemen:

At  your  request,  we  have  examined  Post-Effective  Amendment  No.  1 to the
Registration  Statement on Form S-3 to be filed by  UnionBanCal  Corporation,  a
Delaware   corporation  (the  "Company"),   with  the  Securities  and  Exchange
Commission in connection with the registration under the Securities Act of 1933,
as amended (the "Securities  Act"), of 600,000 shares of common stock, par value
$1.00 per share, of the Company (the "Common  Stock"),  to be issued pursuant to
the UnionBanCal  Corporation Dividend  Reinvestment and Stock Purchase Plan (the
"Plan"),  which shares of Common Stock were registered  under the Securities Act
by   UnionBanCal   Corporation,   a   California   corporation,   prior  to  its
reincorporation in Delaware.  We have examined the proceedings  heretofore taken
and to be taken in connection with the  authorization of the Plan and the Common
Stock to be issued pursuant to and in accordance with the Plan.

Based  upon such  examination  and upon such  matters of fact and law as we have
deemed  relevant,  we are of the  opinion  that the  Common  Stock has been duly
authorized  by all  necessary  corporate  action on the part of the Company and,
when issued in accordance  with such  authorization,  the provisions of the Plan
and relevant  agreements  duly authorized by and in accordance with the terms of
the Plan, will be validly issued,  fully paid and  nonassessable.  We consent to
the use of this opinion as an exhibit to  Post-Effective  Amendment No. 1 to the
above-referenced Registration Statement.

Very truly yours,


/S/ PILLSBURY WINTHROP LLP