<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, 2001

                                       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.)

          One Front 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, 2001

                                TABLE OF CONTENTS

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

 Item 1. Financial Statements


         Balance Sheets - March 31, 2001 (unaudited) and December 31, 2000                         4


         Statements of Operations for the three months ended March 31, 2001 and 2000
         (unaudited)                                                                               5


         Statements of Cash Flows for the three months ended March 31, 2001 and 2000
         (unaudited)                                                                               6


         Notes to 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 balance sheets as of March 31,
        2001 and December 31, 2000, statements of operations for the three
        months ended March 31, 2001 and 2000, and statements of cash flows for
        the three months ended March 31, 2001 and 2000.



                                       3
<PAGE>   4

                            IEA INCOME FUND IX, L.P.

                                 BALANCE SHEETS

<TABLE>
<CAPTION>
                                                                                   March 31,              December 31,
                                                                                     2001                     2000
                                                                                 ------------             ------------
                                                                                 (Unaudited)
<S>                                                                              <C>                      <C>
                 Assets

Current assets:
   Cash and cash equivalents, includes $549,310 at March 31, 2001
      and  $640,874 at December 31, 2000 in interest-bearing accounts            $    585,027             $    741,214
   Net lease receivables due from Leasing Company
      (notes 1 and 2)                                                                  97,340                   98,958
                                                                                 ------------             ------------

         Total current assets                                                         682,367                  840,172
                                                                                 ------------             ------------

Container rental equipment, at cost                                                10,127,216               10,630,601
   Less accumulated depreciation                                                    6,529,866                6,746,246
                                                                                 ------------             ------------
      Net container rental equipment                                                3,597,350                3,884,355
                                                                                 ------------             ------------

         Total assets                                                            $  4,279,717             $  4,724,527
                                                                                 ============             ============

            Partners' Capital

Partners' capital (deficit):
   General partner                                                               $    (74,056)            $    (69,608)
   Limited partners                                                                 4,353,773                4,794,135
                                                                                 ------------             ------------

         Total partners' capital                                                 $  4,279,717             $  4,724,527
                                                                                 ============             ============
</TABLE>


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



                                       4
<PAGE>   5

                            IEA INCOME FUND IX, L.P.

                            STATEMENTS OF OPERATIONS

                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                                       Three Months Ended
                                                                 ------------------------------
                                                                 March 31,             March 31,
                                                                   2001                  2000
                                                                 ---------             ---------
<S>                                                              <C>                   <C>
Net lease revenue (notes 1 and 3)                                $ 223,726             $ 230,703

Other operating expenses:
  Depreciation                                                     118,984               184,159
  Other general and administrative expenses                         21,489                13,225
                                                                 ---------             ---------
                                                                   140,473               197,384
                                                                 ---------             ---------

    Income from operations                                          83,253                33,319

Other income (loss):
  Interest income                                                    7,964                 6,214
  Net loss on disposal of equipment                                (31,610)              (37,319)
                                                                 ---------             ---------
                                                                   (23,646)              (31,105)
                                                                 ---------             ---------
    Net income                                                   $  59,607             $   2,214
                                                                 =========             =========

Allocation of net income (loss):
  General partner                                                $  11,331             $   9,415
  Limited partners                                                  48,276                (7,201)
                                                                 ---------             ---------

                                                                 $  59,607             $   2,214
                                                                 =========             =========

Limited partners' per unit share of net income (loss)            $    1.42             $   (0.21)
                                                                 =========             =========
</TABLE>


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



                                       5
<PAGE>   6

                            IEA INCOME FUND IX, L.P.

                            STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                                      Three Months Ended
                                                                ------------------------------
                                                                March 31,             March 31,
                                                                  2001                  2000
                                                                ---------             ---------
<S>                                                             <C>                   <C>
Net cash provided by operating activities                       $ 227,479             $ 330,376

Cash flows provided by investing activities:
  Proceeds from sale of container rental equipment                120,751               107,714

Cash flows used in financing activities:
  Distribution to partners                                       (504,417)             (320,653)
                                                                ---------             ---------


Net (decrease) increase in cash and cash equivalents             (156,187)              117,437


Cash and cash equivalents at January 1                            741,214               492,680
                                                                ---------             ---------


Cash and cash equivalents at March 31                           $ 585,027             $ 610,117
                                                                =========             =========
</TABLE>


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



                                       6
<PAGE>   7

                                   IEA INCOME FUND IX, L.P.

                           NOTES TO UNAUDITED 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 sold.

        (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, and 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 financial statements.


                                                                     (Continued)



                                       7
<PAGE>   8

                            IEA INCOME FUND IX, L.P.

                     NOTES TO UNAUDITED 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 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 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 financial statements are prepared in conformity with
                accounting principles generally accepted in the United States
                (GAAP), which 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 earned by the Leasing
        Company under operating leases to ocean carriers for the containers
        owned by the Partnership. Net lease receivables at March 31, 2001 and
        December 31, 2000 were as follows:

<TABLE>
<CAPTION>
                                                                   March 31,         December 31,
                                                                     2001                2000
                                                                   --------          ------------
         <S>                                                       <C>               <C>
         Gross lease receivables                                   $397,769            $423,070
         Less:
         Direct operating payables and accrued expenses             147,673             165,794
         Damage protection reserve                                   26,575              29,287
         Base management fees payable                                51,683              51,032
         Reimbursed administrative expenses                          11,905              15,014
         Allowance for doubtful accounts                             62,593              62,985
                                                                   --------            --------

         Net lease receivables                                     $ 97,340            $ 98,958
                                                                   ========            ========
</TABLE>


                                                                     (Continued)



                                       8
<PAGE>   9

                            IEA INCOME FUND IX, L.P.

                     NOTES TO UNAUDITED 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 earned by the Leasing Company under operating leases
        to ocean carriers for the containers owned by the Partnership. Net lease
        revenue for each of the three-month periods ended March 31, 2001 and
        2000 was as follows:

<TABLE>
<CAPTION>
                                                             Three Months Ended
                                                        ----------------------------
                                                        March 31,           March 31,
                                                          2001                2000
                                                        --------            --------
         <S>                                            <C>                 <C>
         Rental revenue                                 $307,010            $391,729
         Less:
         Rental equipment operating expenses              47,483             109,641
         Base management fees                             21,429              25,137
         Reimbursed administrative expenses               14,372              26,248
                                                        --------            --------

                                                        $223,726            $230,703
                                                        ========            ========
</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 leasing marine dry cargo
        containers. As of March 31, 2001, the Partnership operated 1,302
        twenty-foot, 501 forty-foot and 890 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, 2001 and
        December 31, 2000.

        At March 31, 2001, the Registrant had $585,027 in cash and cash
        equivalents, a decrease of $156,187 from the cash balances at December
        31, 2000. Contributing to this decline was the Registrants' results from
        operations, impacted by a declining fleet size and conditions created by
        the slowdown in the global economy.

        During the first three months of 2001, the Registrant disposed of 144
        containers as part of its ongoing container operations. At March 31,
        2001, 56% of the original equipment remained in the Registrant's fleet,
        as compared to 59% at December 31, 2000, 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                        162            116            204
              Master leases                      847            241            491
                                               -----            ---            ---
                 Subtotal                      1,009            357            695

         Containers off lease                    293            144            195
                                               -----            ---            ---

              Total container fleet            1,302            501            890
                                               =====            ===            ===
</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                            1,025          44%        298          38%          763          47%
                                                        -----         ---         ---         ---         -----         ---

         Remaining fleet at March 31, 2001              1,302          56%        501          62%          890          53%
                                                        =====         ===         ===         ===         =====         ===
</TABLE>

        During the first quarter of 2001, distributions from operations and
        sales proceeds amounted to $488,638, reflecting distributions to the
        general and limited partners for the fourth quarter of 2000. This
        represents an increase from the $350,544 distributed during the fourth
        quarter of 2000, reflecting distributions for the third quarter of 2000.
        The increase in distributions was a result of favorable cash collections
        of outstanding receivables and an increase in container sales proceeds
        generated during the fourth quarter of 2000. 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.


                                                                     (Continued)



                                       10
<PAGE>   11

2)      Material changes in the results of operations between the three-month
        period ended March 31, 2001 and the three-month period ended March 31,
        2000.

        In the first quarter of 2001, the worldwide demand for containers was
        significantly impacted by the slowdown in the global economy. These
        conditions are reflected in the decline of the Registrant's utilization
        and per-diem rates from December 31, 2000 levels. The Leasing Company
        has implemented a number of marketing initiatives which are designed to
        target identified leasing opportunities and enhance inventory
        management.

        Net lease revenue for the three-month period ended March 31, 2001 was
        $223,726, a decline of approximately 3% 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, 2001 was $307,010, a
        decline of 22% from the same three-month period in 2000. 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, 2001 declined 4% 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,
        2001 and 2000 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))                             4,188             5,102
        Average utilization                                       79%               79%
</TABLE>

        Depreciation expense declined 35% when compared to the same three-month
        period in the prior year. Rental equipment operating expenses were 15%
        of the Registrant's gross lease revenue during the three-month period
        ended March 31, 2001, as compared to 28% during the three-month period
        ended March 31, 2000, primarily due to the $29,212 reduction in the
        provision for doubtful accounts, and the reduction in fleet size, which
        contributed to a decline in storage and handling expenses, agent fees,
        and recovery costs totaling $19,703. In addition, the Registrant's
        declining fleet size and related operating results contributed to a
        decline in base management and reimbursable administrative fees.

        The Registrant disposed of 144 containers during the first quarter of
        2001, as compared to 141 containers during the first quarter of 2000.
        These disposals resulted in a loss of $31,610 for the first quarter of
        2001, as compared to a loss of $37,319 for the first quarter of 2000.
        The Registrant believes that the net losses on container disposals in
        the first quarters of 2001 and 2000 were a result of various factors
        including the age, condition, suitability for continued leasing, as well
        as the geographical location of the containers when disposed. These
        factors will continue to influence the decision to repair or dispose of
        a container when it is returned by a lessee, as well as the amount of
        sales proceeds received and the related gain or loss on container
        disposals. The level of the Registrant's container disposals in
        subsequent periods will also contribute to fluctuations in the net gain
        or loss on disposals. As a result of current market conditions, the
        Registrant will monitor the carrying value of its containers to
        determine if they have been permanently impaired.


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
</TABLE>


(b)     Reports on Form 8-K

        No reports on Form 8-K were filed by the Registrant during the quarter
        ended March 31, 2001.


----------

*       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



                                       By  /s/ John Kallas
                                           -------------------------------------
                                           John Kallas
                                           Chief Financial Officer and Director
                                           of Cronos Capital Corp. ("CCC")
                                           Principal Financial and Accounting
                                           Officer of CCC

Date: May 15, 2001



                                       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
</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)