Exhibit 32.1



                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002


In  connection  with this  Quarterly  Report  of  UnionBanCal  Corporation  (the
"Company") on Form 10-Q for the quarter  ending March 31, 2004 as filed with the
Securities  and  Exchange  Commission  on the date  hereof  (the  "Report"),  I,
Norimichi Kanari, Chief Executive Officer of the Company,  certify,  pursuant to
18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley
Act of 2002, that, to my knowledge:

     (1)  The Report fully  complies with the  requirements  of Section 13(a) or
          15(d) of the Securities Exchange Act of 1934; and

     (2)  The  information  contained  in the  Report  fairly  presents,  in all
          material respects,  the financial  condition and results of operations
          of the Company.



Dated:  May 10, 2004




                                By:         /S/ NORIMICHI KANARI
                                    --------------------------------------------
                                                Norimichi Kanari
                                            Chief Executive Officer