UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): September 26, 2013

UnionBanCal Corporation

(Exact name of registrant as specified in its charter)

400 California Street

San Francisco, CA 94104-1302

(Address of principal executive offices) (Zip Code)

Tel. (415) 765-2969

Registrant’s telephone number, including area code

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On September 26, 2013, Union Bank, N.A. (the “Bank”), the wholly-owned bank subsidiary of UnionBanCal Corporation, issued $500,000,000 in aggregate principal amount of Floating Rate Senior Bank Notes due 2016 (the “2016 Floating Rate Notes”), $500,000,000 in aggregate principal amount of 1.50% Senior Bank Notes due 2016 (the “2016 Fixed Rate Notes”), and $1,000,000,000 in aggregate principal amount of 2.625% Senior Bank Notes due 2018 (the “2018 Fixed Rate Notes” and, together with the 2016 Floating Rate Notes and the 2016 Fixed Rate Notes, the “Senior Notes”). The 2016 Floating Rate Notes were issued to purchasers at a price of 100% of their principal amount, resulting in net proceeds to the Bank (before expenses) of $498,750,000. The 2016 Fixed Rate Notes were issued to purchasers at a price of 99.746% of their principal amount, resulting in net proceeds to the Bank (before expenses) of $497,480,000. The 2018 Fixed Rate Notes were issued to purchasers at a price of 99.977% of their principal amount, resulting in net proceeds to the Bank (before expenses) of $996,270,000.

The 2016 Floating Rate Notes will bear interest at a rate equal to three-month U.S. Dollar LIBOR plus 0.75% per annum and will mature on September 26, 2016. The 2016 Fixed Rate Notes will bear interest at a rate of 1.50% per annum and will mature on September 26, 2016. The 2018 Fixed Rate Notes will bear interest at a rate of 2.625% per annum and will mature on September 26, 2018. Interest payments are due on the 2016 Floating Rate Notes on March 26, June 26, September 26 and December 26 of each year, commencing on December 26, 2013. Interest payments are due on the 2016 Fixed Rate Notes and the 2018 Fixed Rate Notes on March 26 and September 26 of each year, commencing on March 26, 2014.

The 2016 Floating Rate Notes are not redeemable at the option of the Bank prior to maturity. The Bank may redeem any of the 2016 Fixed Rate Notes, in whole or in part, on and after August 26, 2016 at a redemption price equal to 100% of the principal amount being redeemed plus interest accrued to, but excluding, the date of redemption upon not less than 30 nor more than 60 days’ notice provided by the Bank to holders of the 2016 Fixed Rate Notes. The Bank may redeem any of the 2018 Fixed Rate Notes, in whole or in part, on and after August 26, 2018 at a redemption price equal to 100% of the principal amount being redeemed plus interest accrued to, but excluding, the date of redemption upon not less than 30 nor more than 60 days’ notice provided by the Bank to holders of the 2018 Fixed Rate Notes. None of the Senior Notes are subject to repayment at the option of the holders prior to maturity.

The net proceeds from the sale of the Senior Notes will be used by the Bank for general corporate purposes in the ordinary course of its banking business.

The Senior Notes were issued as part of the Bank’s $8 billion bank note program under which the Bank may issue, from time to time, senior unsecured debt obligations with maturities of more than one year from their respective dates of issue and subordinated debt obligations with maturities of five years or more from their respective dates of issue. After issuing the Senior Notes, there is $2.65 billion available for issuance under the program.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: October 1, 2013