<PAGE>

  AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 12, 2000.



                                                      REGISTRATION NO. 333-44618

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                         ------------------------------


                                AMENDMENT NO. 1
                                       TO
                                    FORM S-1
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933

                         ------------------------------

                                  ADEXA, INC.
             (Exact Name of Registrant as Specified in its Charter)

<TABLE>
<S>                                 <C>                                 <C>
             DELAWARE                              7372                             33-0616222
 (State or Other Jurisdiction of       (Primary Standard Industrial              (I.R.S. Employer
  Incorporation or Organization)       Classification Code Number)            Identification Number)
</TABLE>

                       5933 W. CENTURY BLVD., 12TH FLOOR
                             LOS ANGELES, CA. 90045
                                 (310) 338-8444
  (Address, Including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)
                         ------------------------------

                              DR. K. CYRUS HADAVI
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                  ADEXA, INC.
                       5933 W. CENTURY BLVD., 12TH FLOOR
                             LOS ANGELES, CA. 90045
                                 (310) 338-8444
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)
                         ------------------------------

                                   COPIES TO:

<TABLE>
<S>                                                   <C>
                DAVID T. YOUNG, ESQ.                                 GARY L. SELLERS, ESQ.
           WILLIAM E. GROWNEY, JR., ESQ.                           SIMPSON THACHER & BARTLETT
               DAMON D. JORDAN, ESQ.                                  425 LEXINGTON AVENUE
               DAVID W. WIENER, ESQ.                                NEW YORK, NEW YORK 10017
              GUNDERSON DETTMER STOUGH                                   (212) 455-2000
        VILLENEUVE FRANKLIN & HACHIGIAN, LLP
               155 CONSTITUTION DRIVE
            MENLO PARK, CALIFORNIA 94025
                   (650) 321-2400
</TABLE>

                         ------------------------------

        APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
As soon as practicable after the effective date of this registration statement.
                         ------------------------------

    If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, as amended, check the following box. / /

    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. / / _________

    If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. / / _________

    If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. / /
                         ------------------------------

                        CALCULATION OF REGISTRATION FEE


<TABLE>
<CAPTION>
                                                               PROPOSED MAXIMUM
                   TITLE OF EACH CLASS OF                          AGGREGATE            AMOUNT OF
                SECURITIES TO BE REGISTERED                    OFFERING PRICE(1)   REGISTRATION FEE(2)
<S>                                                           <C>                  <C>
Common stock, no par value..................................      $75,000,000            $19,800
</TABLE>


(1) Estimated solely for the purpose of computing the amount of the registration
    fee pursuant to Rule 457(o).


(2) The registration fee was paid with a previous filing.

                         ------------------------------

    THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT THAT SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF
THE SECURITIES ACT OF 1933, AS AMENDED, OR UNTIL THE REGISTRATION STATEMENT
SHALL BECOME EFFECTIVE ON SUCH DATE AS THE SECURITIES AND EXCHANGE COMMISSION,
ACTING PURSUANT TO SUCH SECTION 8(a), MAY DETERMINE.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>

                                EXPLANATORY NOTE



    This Amendment No. 1 to the Form S-1 Registration Statement is being filed
for the sole purpose of filing additional exhibits.


                                    PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 13.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

    The following table sets forth the costs and expenses, other than
underwriting discounts and commissions, payable by Adexa in connection with the
sale of common stock being registered. All amounts are estimates except the SEC
registration fee and the NASD filing fees.

<TABLE>
<S>                                                           <C>
SEC Registration fee........................................  $19,800
NASD fee....................................................    8,000
Nasdaq National Market listing fee..........................
Printing and engraving expenses.............................
Legal fees and expenses.....................................
Accounting fees and expenses................................
Blue sky fees and expenses..................................
Transfer agent fees.........................................
Miscellaneous fees and expenses.............................
                                                              -------
  Total.....................................................  $
                                                              =======
</TABLE>

ITEM 14.  INDEMNIFICATION OF DIRECTORS AND OFFICERS

    Section 145 of the Delaware General Corporation Law authorizes a court to
award or a corporation's board of directors to grant indemnification to
directors and officers in terms sufficiently broad to permit indemnification
under some circumstances for liabilities (including reimbursement for expenses
incurred) arising under the Securities Act of 1933, as amended (the "Securities
Act"). Article VII, Section 6, of the Registrant's Bylaws provides for mandatory
indemnification of its directors and officers and permissible indemnification of
employees and other agents to the maximum extent permitted by the Delaware
General Corporation Law. The Registrant's Certificate of Incorporation provides
that, pursuant to Delaware law, its directors shall not be liable for monetary
damages for breach of the directors' fiduciary duty as directors to Adexa and
its stockholders. This provision in the Certificate of Incorporation does not
eliminate the directors' fiduciary duty, and in appropriate circumstances
equitable remedies including injunctive or other forms of non-monetary relief
will remain available under Delaware law. In addition, each director will
continue to be subject to liability for breach of the director's duty of loyalty
to Adexa for acts or omissions not in good faith or involving intentional
misconduct, for knowing violations of law, for actions leading to improper
personal benefit to the director, and for payment of dividends or approval of
stock repurchases or redemptions that are unlawful under Delaware law. The
provision also does not affect a director's responsibilities under any other
law, including the federal securities laws or state or federal environmental
laws. The Registrant has entered into Indemnification Agreements with its
officers and directors, a form of which is attached as Exhibit 10.1 hereto and
incorporated herein by reference. The Indemnification Agreements provide the
Registrant's officers and directors with further indemnification to the maximum
extent permitted by the Delaware General Corporation Law." Reference is made to
Section   of the Underwriting Agreement contained in Exhibit 1.1 hereto,
indemnifying officers and directors of the Registrant against some types of
liabilities.

                                      II-1
<PAGE>
ITEM 15.  RECENT SALES OF UNREGISTERED SECURITIES

    In the three years preceding the filing of this registration statement, the
Registrant has issued and sold the following securities:

    - During the period between August 4, 1997 and February 28, 1998, Registrant
      sold an aggregate of 4,130,170 shares of its Series A Preferred Stock to
      19 investors at a purchase price of $1.18 per share.

    - During the period between July 2, 1998 and October 30, 1998, Registrant
      sold an aggregate of 2,492,424 shares of its Series B Preferred Stock to
      19 investors at a purchase price of $3.30 per share.

    - On August 24, 2000, Registrant sold an aggregate of 1,574,801 shares of
      its Series C Preferred Stock to 34 investors at a purchase price of $12.70
      per share.

    - As of August 24, 2000, Registrant has sold and issued 715,036 shares of
      its common stock for an aggregate purchase price of $229,980 to employees
      and consultants pursuant to direct issuance and to exercises of options
      under its 1998 Stock Plan.

    The sale of the above securities was deemed to be exempt from registration
under the Securities Act in reliance upon Section 4(2) of the Securities Act or
Rule 701 promulgated under Section 3(b) of the Securities Act as transactions by
an issuer not involving any public offering or transactions pursuant to
compensation benefit plans and contracts relating to compensation as provided
under Rule 701. The recipients of securities in each transaction represented
their intentions to acquire the securities for investment only and not with a
view to or for sale in connection with any distribution of those securities, and
appropriate legends were affixed to the share certificates issued in those
transactions. All recipients had adequate access, through their relationships
with the Registrant, to information about the Registrant.

ITEM 16.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

(a) EXHIBITS


<TABLE>
<CAPTION>
EXHIBIT NO.             DESCRIPTION
-----------             -----------
<C>                     <S>
        1.1*            Form of Underwriting Agreement

        3.1*            Certificate of Incorporation of the Registrant, as amended
                        to date

        3.2*            Form of Restated Certificate of Incorporation to be filed
                        upon the closing of this offering

        3.3*            Bylaws of the Registrant

        3.4*            Form of Amended and Restated Bylaws to take effect as of the
                        closing of the offering

        4.1*            Reference is made to Exhibits 3.1, 3.2, 3.3 and 3.4

        4.2*            Specimen common stock certificate

        4.3**           Amended and Restated Investors' Rights Agreement

        5.1*            Opinion of Gunderson Dettmer Stough Villeneuve Franklin &
                        Hachigian, LLP

       10.1*            Form of Indemnification Agreement

       10.2**           Lease between the Registrant and Haseko Corporation, a
                        Japanese corporation, dated June 20, 1996, as amended

       10.3**           Lease between the Registrant and 20 Adelaide St. East, a
                        co-ownership, dated August 30, 1999

       10.4**           1998 Stock Plan
</TABLE>


                                      II-2
<PAGE>


<TABLE>
<CAPTION>
EXHIBIT NO.             DESCRIPTION
-----------             -----------
<C>                     <S>
       10.5**           2000 Stock Incentive Plan

       10.6**           2000 Employee Stock Purchase Plan

       10.7**           Promissory note from K. Cyrus Hadavi to the Company dated
                        July 31, 1997

       10.8**           Promissory note from Udo Dangler to the Company dated
                        May 19, 2000

       10.9**           Loan from Silicon Valley Bank to the Company dated
                        August 22, 2000

       10.10+           Software Teaming Agreement between the Registrant and Compaq
                        Computer Corporation dated October 26, 1999

       10.11+           Solution Provider Agreement between the Registrant and
                        Hewlett Packard Japan, Ltd. dated September 1, 1999, as
                        amended

       10.12+           Value Added Reseller Agreement between the Registrant and
                        QAD Inc. dated April 14, 1998

       23.1**           Consent of Independent Accountants

       23.2*            Consent of Counsel. Reference is made to Exhibit 5.1

       24.1**           Power of Attorney

       27.1**           Financial Data Schedule

       99.1             Artwork for Inside Cover Page of Prospectus
</TABLE>


------------------------

  * To be filed by amendment.


 ** Previously filed



  + Confidential treatment has been requested for certain portions which have
    been blacked out in the copy of the exhibit filed with the Securities and
    Exchange Commission. The omitted information has been filed separately with
    the Securities and Exchange Commission pursuant to the application for
    confidential treatment.


(b) FINANCIAL STATEMENT SCHEDULES

    Schedule VIII--Valuation and Qualifying Accounts

    Schedules not listed above have been omitted because the information
required to be presented therein is not applicable or is shown in the financial
statements or notes thereto.

ITEM 17.  UNDERTAKINGS

    The Registrant undertakes to provide to the Underwriters at the closing
specified in the Underwriting Agreement, certificates in the denominations and
registered in the names required by the Underwriters to permit prompt delivery
to each purchaser.

    Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the Delaware General Corporation Law, the Certificate of
Incorporation or the Bylaws of the Registrant, the Underwriting Agreement, or
otherwise, the Registrant has been advised that in the opinion of the Securities
and Exchange Commission this indemnification is against public policy as
expressed in the Securities Act, and is, therefore, unenforceable. In the event
that a claim for indemnification against these liabilities (other than the
payment by the Registrant of expenses incurred or paid by a director, officer,
or controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by an director, officer or controlling person in
connection with the securities being registered

                                      II-3
<PAGE>
hereunder, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question of whether the indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of that issue.

    The Registrant undertakes that:

    (1) For purposes of determining any liability under the Securities Act, the
information omitted from the form of prospectus filed as part of this
registration statement in reliance upon Rule 430A and contained in a form of
prospectus filed by the Registrant pursuant to Rule 424(b)(1) or (4) or 497(h)
under the Securities Act shall be deemed to be part of this registration
statement as of the time it was declared effective.

    (2) For the purpose of determining any liability under the Securities Act,
each post-effective amendment that contains a form of prospectus shall be deemed
to be a new registration statement relating to the securities offered therein,
and the offering of the securities at that time shall be deemed to be its
initial bona fide offering.

                                      II-4
<PAGE>
                                   SIGNATURES


    Pursuant to the requirements of the Securities Act of 1933, as amended, the
registrant has duly caused this Amendment No. 1 to the Registration Statement to
be signed on its behalf by the undersigned, thereunto duly authorized, in the
City of Los Angeles, State of California, on this 12th day of September, 2000.



<TABLE>
<S>                                                    <C>   <C>
                                                       ADEXA, INC.

                                                       By:               /s/ K. CYRUS HADAVI
                                                             ------------------------------------------
                                                                           K. Cyrus Hadavi
                                                                PRESIDENT AND CHIEF EXECUTIVE OFFICER
</TABLE>



    PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED, THIS
AMENDMENT NO. 1 TO THE REGISTRATION STATEMENT HAS BEEN SIGNED BY THE FOLLOWING
PERSONS IN THE CAPACITIES AND ON THE DATES INDICATED:



<TABLE>
<C>                                            <S>                                 <C>
             /s/ K. CYRUS HADAVI               President and Chief Executive       September 12,
    ------------------------------------         Officer (Principal Executive      2000
               K. Cyrus Hadavi                   Officer) and Director

            /s/ J. TIMOTHY ROMER               Chief Financial Officer (Principal  September 12,
    ------------------------------------         Financial and Accounting          2000
              J. Timothy Romer                   Officer)

             /s/ DAVID R. GOLOB*               Director                            September 12,
    ------------------------------------                                           2000
               David R. Golob

           /s/ WILLIAM W. LATTIN*              Director                            September 12,
    ------------------------------------                                           2000
              William W. Lattin

               /s/ SAM H. LEE*                 Director                            September 12,
    ------------------------------------                                           2000
                 Sam H. Lee

        /s/ WILLIAM H. YOUNGER, JR.*           Director                            September 12,
    ------------------------------------                                           2000
           William H. Younger, Jr.
</TABLE>



<TABLE>
<S>    <C>                                        <C>                                  <C>
*By:              /s/ K. CYRUS HADAVI                                                  September 12,
           --------------------------------                                            2000
                    K. Cyrus Hadavi
                   ATTORNEY-IN-FACT

*By:             /s/ J. TIMOTHY ROMER                                                  September 12,
           --------------------------------                                            2000
                   J. Timothy Romer
                   ATTORNEY-IN-FACT
</TABLE>


                                      II-5
<PAGE>
                               INDEX TO EXHIBITS


<TABLE>
<CAPTION>
EXHIBIT NO.             DESCRIPTION
-----------             -----------
<C>                     <S>
        1.1*            Form of Underwriting Agreement

        3.1*            Certificate of Incorporation of the Registrant, as amended
                        to date

        3.2*            Form of Restated Certificate of Incorporation to be filed
                        upon the closing of this offering

        3.3*            Bylaws of the Registrant

        3.4*            Form of Amended and Restated Bylaws to take effect as of the
                        closing of the offering

        4.1*            Reference is made to Exhibits 3.1, 3.2, 3.3 and 3.4

        4.2*            Specimen common stock certificate

        4.3**           Amended and Restated Investors' Rights Agreement

        5.1*            Opinion of Gunderson Dettmer Stough Villeneuve Franklin &
                        Hachigian, LLP

       10.1*            Form of Indemnification Agreement

       10.2**           Lease between the Registrant and Haseko Corporation, a
                        Japanese corporation, dated June 20, 1996, as amended

       10.3**           Lease between the Registrant and 20 Adelaide St. East, a
                        co-ownership, dated August 30, 1999

       10.4**           1998 Stock Plan

       10.5**           2000 Stock Incentive Plan

       10.6**           2000 Employee Stock Purchase Plan

       10.7**           Promissory note from K. Cyrus Hadavi to the Company dated
                        July 31, 1997

       10.8**           Promissory note from Udo Dangler to the Company dated
                        May 19, 2000

       10.9**           Loan from Silicon Valley Bank to the Company dated
                        August 22, 2000

       10.10+           Software Teaming Agreement between the Registrant and Compaq
                        Computer Corporation dated October 26, 1999

       10.11+           Solution Provider Agreement between the Registrant and
                        Hewlett Packard Japan, Ltd. dated September 1, 1999, as
                        amended

       10.12+           Value Added Reseller Agreement between the Registrant and
                        QAD Inc. dated April 14, 1998

       23.1**           Consent of Independent Accountants

       23.2*            Consent of Counsel. Reference is made to Exhibit 5.1

       24.1**           Power of Attorney

       27.1**           Financial Data Schedule

       99.1             Artwork for Inside Cover Page of Prospectus
</TABLE>


------------------------

  * To be filed by amendment.


 ** Previously filed



  + Confidential treatment has been requested for certain portions which have
    been blacked out in the copy of the exhibit filed with the Securities and
    Exchange Commission. The omitted information has been filed separately with
    the Securities and Exchange Commission pursuant to the application for
    confidential treatment.