<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                    FORM 10-Q


[X]  QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
     ACT OF 1934 FOR THE QUARTERLY PERIOD ENDED MARCH 31, 2000

                                       OR

[ ]  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
     EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM        TO
                                                        --------  --------


                         Commission file number 0-18169

                            IEA INCOME FUND IX, L.P.
             (Exact name of registrant as specified in its charter)


            California                                           94-3069954
  (State or other jurisdiction of                             (I.R.S. Employer
  incorporation or organization)                             Identification No.)


         444 Market Street, 15th Floor, San Francisco, California      94111
                 (Address of principal executive offices)            (Zip Code)

                                 (415) 677-8990
              (Registrant's telephone number, including area code)


Indicate by check mark whether the registrant (1) has filed all reports required
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. Yes [X] No [ ]


<PAGE>   2
                            IEA INCOME FUND IX, L.P.

                  REPORT ON FORM 10-Q FOR THE QUARTERLY PERIOD
                              ENDED MARCH 31, 2000

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>


                                                                                                                 PAGE
<S>      <C>                                                                                                     <C>
PART I - FINANCIAL INFORMATION

 Item 1. Financial Statements


         Condensed Balance Sheets - March 31, 2000 and December 31, 1999 (unaudited)                              4


         Condensed Statements of Operations for the three months ended March 31, 2000 and 1999 (unaudited)        5


         Condensed Statements of Cash Flows for the three months ended March 31, 2000 and 1999 (unaudited)        6


         Notes to Condensed Financial Statements (unaudited)                                                      7


 Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations                   10


 Item 3. Quantitative and Qualitative Disclosures About Market Risk                                              11


PART II - OTHER INFORMATION


 Item 6. Exhibits and Reports on Form 8-K                                                                        12
</TABLE>


                                       2

<PAGE>   3


                         PART I - FINANCIAL INFORMATION


 Item 1. Financial Statements

         Presented herein are the Registrant's condensed balance sheets as of
         March 31, 2000 and December 31, 1999, condensed statements of
         operations for the three months ended March 31, 2000 and 1999, and
         condensed statements of cash flows for the three months ended March 31,
         2000 and 1999.

                                       3
<PAGE>   4

                            IEA INCOME FUND IX, L.P.

                            CONDENSED BALANCE SHEETS

                                   (UNAUDITED)


<TABLE>
<CAPTION>

                                                                             March 31,         December 31,
                                                                               2000                1999
                                                                           -------------       -------------
<S>                                                                        <C>                 <C>

                 Assets

Current assets:

   Cash and cash equivalents, includes $610,002 at March 31, 2000 and
      $492,580 at December 31, 1999 in interest-bearing accounts           $     610,117       $     492,680

   Net lease receivables due from Leasing Company
      (notes 1 and 2)                                                            151,233             184,713
                                                                           -------------       -------------

         Total current assets                                                    761,350             677,393
                                                                           -------------       -------------

Container rental equipment, at cost                                           12,362,146          12,927,344
   Less accumulated depreciation                                               7,367,165           7,529,966
                                                                           -------------       -------------
      Net container rental equipment                                           4,994,981           5,397,378
                                                                           -------------       -------------

        Total assets                                                       $   5,756,331       $   6,074,771
                                                                           =============       =============
            Partners' Capital

Partners' capital (deficit):
   General partner                                                         $     (59,291)      $     (56,106)
   Limited partners                                                            5,815,622           6,130,877
                                                                           -------------       -------------

         Total partners' capital                                           $   5,756,331       $   6,074,771
                                                                           =============       =============
</TABLE>

              The accompanying notes are an integral part of these
                        condensed financial statements.

                                       4

<PAGE>   5


                            IEA INCOME FUND IX, L.P.

                       CONDENSED STATEMENTS OF OPERATIONS

                                   (UNAUDITED)


<TABLE>
<CAPTION>

                                                              Three Months Ended
                                                           -------------------------
                                                           March 31,       March 31,
                                                             2000            1999
                                                           ---------       ---------
<S>                                                        <C>             <C>
Net lease revenue (notes 1 and 3)                          $ 230,703       $ 342,744

Other operating expenses:
  Depreciation                                               184,159         206,787
  Other general and administrative expenses                   13,225          14,144
                                                           ---------       ---------
                                                             197,384         220,931
                                                           ---------       ---------

    Income from operations                                    33,319         121,813

Other income (loss):
  Interest income                                              6,214           8,245
  Net loss on disposal of equipment                          (37,319)        (61,909)
                                                           ---------       ---------
                                                             (31,105)        (53,664)
                                                           ---------       ---------

    Net income                                             $   2,214       $  68,149
                                                           =========       =========

Allocation of net income (loss):
  General partner                                          $   9,415       $  18,572
  Limited partners                                            (7,201)         49,577
                                                           ---------       ---------

                                                           $   2,214       $  68,149
                                                           =========       =========


Limited partners' per unit share of net income (loss)      $   (0.21)      $    1.46
                                                           =========       =========
</TABLE>


              The accompanying notes are an integral part of these
                        condensed financial statements.


                                       5

<PAGE>   6

                            IEA INCOME FUND IX, L.P.

                       CONDENSED STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)
<TABLE>
<CAPTION>

                                                             Three Months Ended
                                                          --------------------------
                                                          March 31,       March 31,
                                                            2000            1999
                                                          ---------       ---------
<S>                                                       <C>             <C>
Net cash provided by operating activities                 $ 330,376       $ 345,035

Cash flows provided by investing activities:
  Proceeds from sale of container rental equipment          107,714         165,247

Cash flows used in financing activities:
  Distribution to partners                                 (320,653)       (533,104)
                                                          ---------       ---------


Net increase (decrease) in cash and cash equivalents        117,437         (22,822)


Cash and cash equivalents at January 1                      492,680         780,429
                                                          ---------       ---------


Cash and cash equivalents at March 31                     $ 610,117       $ 757,607
                                                          =========       =========
</TABLE>

              The accompanying notes are an integral part of these
                        condensed financial statements.


                                       6
<PAGE>   7
                            IEA INCOME FUND IX, L.P.

               NOTES TO UNAUDITED CONDENSED FINANCIAL STATEMENTS



(1)  Summary of Significant Accounting Policies

     (a) Nature of Operations

         IEA Income Fund IX, L.P. (the "Partnership") is a limited partnership
         organized under the laws of the State of California on June 8, 1988 for
         the purpose of owning and leasing marine cargo containers worldwide to
         ocean carriers. To this extent, the Partnership's operations are
         subject to the fluctuations of world economic and political conditions.
         Such factors may affect the pattern and levels of world trade. The
         Partnership believes that the profitability of, and risks associated
         with, leases to foreign customers is generally the same as those of
         leases to domestic customers. The Partnership's leases generally
         require all payments to be made in United States currency.

         Cronos Capital Corp. ("CCC") is the general partner and, with its
         affiliate Cronos Containers Limited (the "Leasing Company"), manages
         the business of the Partnership. CCC and the Leasing Company also
         manage the container leasing business for other partnerships affiliated
         with the general partner. The Partnership shall continue until December
         31, 2009, unless sooner terminated upon the occurrence of certain
         events.

         The Partnership commenced operations on December 5, 1988, when the
         minimum subscription proceeds of $1,000,000 were obtained. The
         Partnership offered 40,000 units of limited partnership interest at
         $500 per unit, or $20,000,000. The offering terminated on September 11,
         1989, at which time 33,992 limited partnership units had been
         purchased.

     (b) Leasing Company and Leasing Agent Agreement

         Pursuant to the Limited Partnership Agreement of the Partnership, all
         authority to administer the business of the Partnership is vested in
         CCC. CCC has entered into a Leasing Agent Agreement whereby the Leasing
         Company has the responsibility to manage the leasing operations of all
         equipment owned by the Partnership. Pursuant to the Agreement, the
         Leasing Company is responsible for leasing, managing and re-leasing the
         Partnership's containers to ocean carriers, and has full discretion
         over which ocean carriers and suppliers of goods and services it may
         deal with. The Leasing Agent Agreement permits the Leasing Company to
         use the containers owned by the Partnership, together with other
         containers owned or managed by the Leasing Company and its affiliates,
         as part of a single fleet operated without regard to ownership. Since
         the Leasing Agent Agreement meets the definition of an operating lease
         in Statement of Financial Accounting Standards (SFAS) No. 13, it is
         accounted for as a lease under which the Partnership is lessor and the
         Leasing Company is lessee.

         The Leasing Agent Agreement generally provides that the Leasing Company
         will make payments to the Partnership based upon rentals collected from
         ocean carriers after deducting direct operating expenses and management
         fees to CCC. The Leasing Company leases containers to ocean carriers,
         generally under operating leases which are either master leases or term
         leases (mostly one to five years). Master leases do not specify the
         exact number of containers to be leased or the term that each container
         will remain on hire but allow the ocean carrier to pick up and drop off
         containers at various locations; rentals are based upon the number of
         containers used and the applicable per-diem rate. Accordingly, rentals
         under master leases are all variable and contingent upon the number of
         containers used. Most containers are leased to ocean carriers under
         master leases; leasing agreements with fixed payment terms are not
         material to the financial statements. Since there are no material
         minimum lease rentals, no disclosure of minimum lease rentals is
         provided in these condensed financial statements.


                                       7
<PAGE>   8


                            IEA INCOME FUND IX, L.P.

               NOTES TO UNAUDITED CONDENSED FINANCIAL STATEMENTS


     (c) Basis of Accounting

         The Partnership utilizes the accrual method of accounting. Net lease
         revenue is recorded by the Partnership in each period based upon its
         leasing agent agreement with the Leasing Company. Net lease revenue is
         generally dependent upon operating lease rentals from operating lease
         agreements between the Leasing Company and its various lessees, less
         direct operating expenses and management fees due in respect of the
         containers specified in each operating lease agreement.

     (d) Financial Statement Presentation

         These condensed financial statements have been prepared without audit.
         Certain information and footnote disclosures normally included in
         financial statements prepared in accordance with generally accepted
         accounting procedures have been omitted. It is suggested that these
         condensed financial statements be read in conjunction with the
         financial statements and accompanying notes in the Partnership's latest
         annual report on Form 10-K.

         The preparation of financial statements in conformity with accounting
         principles generally accepted in the United States (GAAP) requires the
         Partnership to make estimates and assumptions that affect the reported
         amounts of assets and liabilities and disclosure of contingent assets
         and liabilities at the date of the financial statements and the
         reported amounts of revenues and expenses during the reported period.
         Actual results could differ from those estimates.

         The interim financial statements presented herewith reflect all
         adjustments of a normal recurring nature which are, in the opinion of
         management, necessary to a fair statement of the financial condition
         and results of operations for the interim periods presented. The
         results of operations for such interim periods are not necessarily
         indicative of the results to be expected for the full year.


(2)  Net Lease Receivables Due from Leasing Company

     Net lease receivables due from the Leasing Company are determined by
     deducting direct operating payables and accrued expenses, base management
     fees payable, and reimbursed administrative expenses payable to CCC and its
     affiliates from the rental billings payable by the Leasing Company to the
     Partnership under operating leases to ocean carriers for the containers
     owned by the Partnership. Net lease receivables at March 31, 2000 and
     December 31, 1999 were as follows:

<TABLE>
<CAPTION>

                                                      March 31,        December 31,
                                                         2000               1999
                                                    -------------      -------------
<S>                                                 <C>                <C>
Gross lease receivables                             $     562,706      $     526,631
Less:
Direct operating payables and accrued expenses            205,045            164,098
Damage protection reserve                                  44,336             44,497
Base management fees payable                               50,603             58,250
Reimbursed administrative expenses                         13,874              6,673
Allowance for doubtful accounts                            97,615             68,400
                                                    -------------      -------------

Net lease receivables                               $     151,233      $     184,713
                                                    =============      =============
</TABLE>


                                       8


<PAGE>   9

                            IEA INCOME FUND IX, L.P.

               NOTES TO UNAUDITED CONDENSED FINANCIAL STATEMENTS


(3)  Net Lease Revenue

     Net lease revenue is determined by deducting direct operating expenses,
     base management fees and reimbursed administrative expenses to CCC from the
     rental revenue billed by the Leasing Company under operating leases to
     ocean carriers for the containers owned by the Partnership. Net lease
     revenue for the three-month periods ended March 31, 2000 and 1999 was as
     follows:

<TABLE>
<CAPTION>

                                            Three Months Ended
                                         -------------------------
                                          March 31,      March 31,
                                           2000           1999
                                         ---------      ---------
<S>                                      <C>            <C>
Rental revenue (note 4)                  $ 391,729      $ 498,090
Less:
Rental equipment operating expenses        109,641         94,475
Base management fees                        25,137         36,374
Reimbursed administrative expenses          26,248         24,497
                                         ---------      ---------

                                         $ 230,703      $ 342,744
                                         =========      =========
</TABLE>

(4)  Operating Segment

     The Financial Accounting Standards Board has issued SFAS No. 131,
     "Disclosures about Segments of an Enterprise and Related Information,"
     which changes the way public business enterprises report financial and
     descriptive information about reportable operating segments. An operating
     segment is a component of an enterprise that engages in business activities
     from which it may earn revenues and incur expenses, whose operating results
     are regularly reviewed by the enterprise's chief operating decision maker
     to make decisions about resources to be allocated to the segment and assess
     its performance, and about which separate financial information is
     available. Management operates the Partnership's container fleet as a
     homogenous unit and has determined, after considering the requirements of
     SFAS No. 131, that as such it has a single reportable operating segment.

     The Partnership derives its revenues from marine dry cargo containers. As
     of March 31, 2000, the Partnership operated 1,672 twenty-foot, 583
     forty-foot and 1,067 forty-foot high-cube marine dry cargo containers.

     Due to the Partnership's lack of information regarding the physical
     location of its fleet of containers when on lease in the global shipping
     trade, it is impracticable to provide the geographic area information
     required by SFAS No. 131.

                                     ******

                                       9
<PAGE>   10

Item 2. Management's Discussion and Analysis of Financial Condition and Results
        of Operations


It is suggested that the following discussion be read in conjunction with the
Registrant's most recent annual report on Form 10-K.


1)   Material changes in financial condition between March 31, 2000 and December
     31, 1999.

     During the first three months of 2000, the Registrant disposed of 141
     containers as part of its ongoing container operations. At March 31, 2000,
     70% of the original equipment remained in the Registrant's fleet, as
     compared to 72% at December 31, 1999, and was comprised of the following:

<TABLE>
<CAPTION>

                                                               40-Foot
                                 20-Foot        40-Foot       High-Cube
                                ---------      ---------      ---------
<S>                             <C>            <C>            <C>
Containers on lease:
     Term leases                      132             95            197
     Master leases                  1,212            361            671
                                ---------      ---------      ---------
        Subtotal                    1,344            456            868

Containers off lease                  328            127            199
                                ---------      ---------      ---------

     Total container fleet          1,672            583          1,067
                                =========      =========      =========
</TABLE>


<TABLE>
<CAPTION>


                                                                                        40-Foot
                                           20-Foot                40-Foot               High-Cube
                                       ---------------        ----------------       -----------------
                                       Units        %         Units        %         Units        %
                                       -----      -----       -----      -----       -----      -----
<S>                                    <C>        <C>         <C>        <C>         <C>        <C>
Total purchases                        2,327        100%        799        100%      1,653        100%
     Less disposals                      655         28%        216         27%        586         35%
                                       -----      -----       -----      -----       -----      -----


Remaining fleet at March 31, 2000      1,672         72%        583         73%      1,067         65%
                                       =====      =====       =====      =====       =====      =====
</TABLE>

     The Registrant's allowance for doubtful accounts increased from $68,400 at
     December 31, 1999 to $97,615 at March 31, 2000. This increase was
     attributable to the delinquent account receivable balances of approximately
     14 lessees. The Leasing Company has either negotiated specific payment
     terms with these lessees or is pursuing other alternatives to collect the
     outstanding balances. In each instance, the Registrant believes it has
     provided sufficient reserves for all doubtful accounts.

     During the first quarter of 2000, distributions from operations and sales
     proceeds amounted to $320,653, reflecting distributions to the general and
     limited partners for the fourth quarter of 1999. This represents a decrease
     from the $533,104 distributed during the fourth quarter of 1999, reflecting
     distributions for the third quarter of 1999. The Registrant's continuing
     disposal of containers should produce lower operating results and,
     consequently, lower distributions to its partners in subsequent periods.
     Sales proceeds distributed to its partners may fluctuate in subsequent
     periods, reflecting the level of container disposals.

     In order to take advantage of improving market conditions and stronger
     demand for leased containers, the Registrant undertook a strategy that was
     aimed at significantly reducing its inventory of idle equipment in some
     low-demand locations while, at the same time, fulfilling lessee container
     requirements. As part of this strategy, the Registrant offered leasing
     incentives to several lessees for picking up off-hire equipment from the
     Registrant's higher inventory areas. This not only resulted in stronger
     utilization of the Registrant's equipment, but it also significantly
     lowered Partnership expenses related to storage and handling.

                                       10

<PAGE>   11

2)   Material changes in the results of operations between the three-month
     period ended March 31, 2000 and the three-month period ended March 31,
     1999.

     Net lease revenue for the three-month period ended March 31, 2000 was
     $230,703, a decline of approximately 33% from the same three-month period
     in the prior year. Gross rental revenue (a component of net lease revenue)
     for the three-month period ended March 31, 2000 was $391,729, a decline of
     21% from the same three-month period in 1999. Gross rental revenue was
     primarily impacted by a smaller fleet size and lower per-diem rental rates.
     Average per-diem rental rates for the three-month period ended March 31,
     2000 declined 14% when compared to the same three-month period in the prior
     year. The Registrant's average fleet size and utilization rates for the
     three-month periods ended March 31, 2000 and 1999 were as follows:

<TABLE>
<CAPTION>

                                                    Three Months Ended
                                                 -------------------------
                                                 March 31,       March 31,
                                                    2000            1999
                                                 ---------       ---------
<S>                                              <C>             <C>
Average fleet size (measured in twenty-foot
   equivalent units (TEU))                           5,102           5,712

Average utilization                                     79%             77%
</TABLE>

     The Registrant's declining fleet size contributed to a 11% decline in
     depreciation expense when compared to the same three-month period in the
     prior year. Rental equipment operating expenses were 28% of the
     Registrant's gross lease revenue during the three-month period ended March
     31, 2000, as compared to 19% during the three-month period ended March 31,
     1999.

     YEAR 2000

     The Registrant relies upon the financial and operational systems provided
     by the Leasing Company and its affiliates, as well as the systems provided
     by other independent third parties to service the three primary areas of
     its business: investor processing/maintenance; container leasing/asset
     tracking; and accounting/finance. Neither the Registrant nor the Leasing
     Company experienced nor do they currently anticipate any material adverse
     effects on the Registrant's business, results of operations or financial
     condition as a result of Year 2000 issues involving internal use systems,
     third party products or any of their software products. Costs incurred in
     preparing for Year 2000 issues were expensed as incurred. Neither the
     Registrant nor the Leasing Company anticipate any additional material costs
     in connection with Year 2000 uncertainties. Pursuant to the Limited
     Partnership Agreement, CCC or the Leasing Company, may not seek
     reimbursement of data processing costs associated with the Year 2000
     program.



Item 3. Quantitative and Qualitative Disclosures About Market Risk

        Not applicable.


                                       11
<PAGE>   12


                           PART II - OTHER INFORMATION


Item 6. Exhibits and Reports on Form 8-K

(a)  Exhibits
<TABLE>
<CAPTION>

  Exhibit
    No.                        Description                         Method of Filing
  ------      -------------------------------------------------    -------------------
<S>           <C>                                                  <C>

   3(a)       Limited Partnership  Agreement of the Registrant,    *
              amended and restated as of September 12, 1988


   3(b)       Certificate   of  Limited   Partnership   of  the    **
              Registrant


   27         Financial Data Schedule                              Filed with this document
</TABLE>



(b)  Reports on Form 8-K

     No reports on Form 8-K were filed by the Registrant during the quarter
ended March 31, 2000.



-------------
*     Incorporated by reference to Exhibit "A" to the Prospectus of the
      Registrant dated September 12, 1988, included as part of Registration
      Statement on Form S-1 (No. 33-23321)

**    Incorporated by reference to Exhibit 3.4 to the Registration Statement on
      Form S-1 (No. 33-23321)

                                       12
<PAGE>   13


                                   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 thereunto duly authorized.




                                     IEA INCOME FUND IX, L.P.


                                     By  Cronos Capital Corp.
                                         The General Partner




                                     By  /s/ Dennis J. Tietz
                                      -------------------------------------
                                         Dennis J. Tietz
                                         President and Director of Cronos
                                         Capital Corp.("CCC")
                                         Principal Executive Officer of CCC




Date: May 15, 2000



                                       13
<PAGE>   14

                                  EXHIBIT INDEX


<TABLE>
<CAPTION>

  Exhibit
    No.                        Description                         Method of Filing
  ------      -------------------------------------------------    -------------------
<S>           <C>                                                  <C>

   3(a)       Limited Partnership  Agreement of the Registrant,    *
              amended and restated as of September 12, 1988


   3(b)       Certificate   of  Limited   Partnership   of  the    **
              Registrant


   27         Financial Data Schedule                              Filed with this document
</TABLE>




-------------
*     Incorporated by reference to Exhibit "A" to the Prospectus of the
      Registrant dated September 12, 1988, included as part of Registration
      Statement on Form S-1 (No. 33-23321)

**    Incorporated by reference to Exhibit 3.4 to the Registration Statement on
      Form S-1 (No. 33-23321)