<PAGE>
 
                      SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                        
                                  FORM 10-K/A
                          Amendment No. 1 to Form 10-K
(Mark one)
(X)  Annual report pursuant to section 13 or 15(d) of the Securities Exchange
     Act of 1934 (Fee Required) for the fiscal year ended April 30, 1998 or
(_)  Transition report pursuant to section 13 or 15(d) of the Securities
     Exchange Act of 1934 No Fee Required) for the transition period 
     from __ to __

Commission file number 1-10711
                       -------

                          SIZZLER INTERNATIONAL, INC.
             (Exact name of registrant as specified in its charter)

             Delaware                               95-4307254
  -------------------------------                ------------------
  (State or Other Jurisdiction of                 (I.R.S. Employer
  Incorporation or Organization)                 Identification No.)
  

           6101 West Centinela Avenue, Culver City, California 90230
           ---------------------------------------------------------
         (Address of principal executive offices, including zip code)

Registrant's telephone number, including area code:  (310) 568-0135

Securities registered pursuant to Section 12(b) of the Act:

                                           NAME OF EACH EXCHANGE ON
       TITLE OF EACH CLASS                     WHICH REGISTERED
       -------------------                     ----------------
       Common Stock, $.01 Par Value        New York Stock Exchange

Securities registered pursuant to Section 12(g) of the Act:

                                     NONE
                                --------------
                                (TITLE OF CLASS)

Indicate by check mark whether the registrant (1) has filed all reports to be
filed by section 13 or 15(d) of the Securities Exchange Act of 1934 during the
preceding 12 months (or for such shorter period that the registrant was required
to file such reports), and (2) has been subject to such filing requirements for
the past 90 days.

|X| YES  |_| NO

The aggregate market value of the voting stock held by non-affiliates of the
registrant on June 30, 1998, computed by reference to the closing sale price of
such shares on such date was $67,190,827.

The number of shares outstanding of common stock, $0.01 par value, as of June
30, 1998, was 28,823,249.

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of the Form 10-K or any amendment to this
Form 10-K. [X]

The undersigned registrant hereby amends Exhibit 23 to its Annual Report on Form
10-K as set forth below:
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SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Registrant had duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.

Dated:  October 28, 1998             SIZZLER INTERNATIONAL, INC.

                                     By: /s/ James A. Collins
                                        ------------------------
                                             James A. Collins
                                        Chief Executive Officer


                                     By: /s/ Ryan S. Tondro
                                        -----------------------
                                             Ryan S.Tondro
                                             Vice President
                                        (Principal Financial Officer)