<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 0-21518

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


           California                                             94-3143940
(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 XII, 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 XII, L.P.

                                 BALANCE SHEETS

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

Current assets:
   Cash and cash equivalents, includes $1,351,897 at March 31, 2001
      and $1,287,792 at December 31, 2000 in interest-bearing accounts                         $ 1,455,856             $  1,512,512
   Net lease receivables due from Leasing Company
      (notes 1 and 2)                                                                              444,643                  517,461
                                                                                              ------------             ------------

         Total current assets                                                                    1,900,499                2,029,973
                                                                                              ------------             ------------

Container rental equipment, at cost                                                             59,514,044               59,984,866
   Less accumulated depreciation                                                                29,335,641               28,750,701
                                                                                              ------------             ------------
      Net container rental equipment                                                            30,178,403               31,234,165
                                                                                              ------------             ------------

         Total assets                                                                         $ 32,078,902             $ 33,264,138
                                                                                              ============             ============

            Partners' Capital

Partners' capital (deficit):
   General partner                                                                                (166,478)                (154,625)
   Limited partners                                                                             32,245,380               33,418,763
                                                                                              ------------             ------------

         Total partners' capital                                                              $ 32,078,902             $ 33,264,138
                                                                                              ============             ============
</TABLE>


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



                                       4
<PAGE>   5

                            IEA INCOME FUND XII, 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)                       $ 913,111             $ 954,521

Other operating expenses:
  Depreciation                                            871,884               905,763
  Other general and administrative expenses                45,125                30,483
                                                        ---------             ---------
                                                          917,009               936,246
                                                        ---------             ---------

    Income (loss) from operations                          (3,898)               18,275

Other income (loss):
  Interest income                                          18,080                14,719
  Net loss on disposal of equipment                       (93,287)              (40,776)
                                                        ---------             ---------
                                                          (75,207)              (26,057)
                                                        ---------             ---------

    Net loss                                            $ (79,105)            $  (7,782)
                                                        =========             =========

Allocation of net income (loss):
  General partner                                       $  34,345             $  38,756
  Limited partners                                       (113,450)              (46,538)
                                                        ---------             ---------

                                                        $ (79,105)            $  (7,782)
                                                        =========             =========

Limited partners' per unit share of net loss            $   (0.03)            $   (0.01)
                                                        =========             =========
</TABLE>


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



                                       5
<PAGE>   6

                            IEA INCOME FUND XII, 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                       $   844,645             $ 1,195,206


Cash flows provided by investing activities:
  Proceeds from disposal of equipment                               204,830                  76,656


Cash flows used in financing activities:
  Distribution to partners                                       (1,106,131)             (1,222,253)
                                                                -----------             -----------


Net (decrease) increase in cash and cash equivalents                (56,656)                 49,609


Cash and cash equivalents at January 1                            1,512,512               1,111,425
                                                                -----------             -----------


Cash and cash equivalents at March 31                           $ 1,455,856             $ 1,161,034
                                                                ===========             ===========
</TABLE>


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



                                       6
<PAGE>   7

                            IEA INCOME FUND XII, L.P.

                     NOTES TO UNAUDITED FINANCIAL STATEMENTS


(1)     Summary of Significant Accounting Policies

        (a)     Nature of Operations

                IEA Income Fund XII, L.P. (the "Partnership") is a limited
                partnership organized under the laws of the State of California
                on August 28, 1991 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, 2011, unless
                sooner terminated upon the occurrence of certain events.

                The Partnership commenced operations on January 31, 1992, when
                the minimum subscription proceeds of $2,000,000 were obtained.
                The Partnership offered 3,750,000 units of limited partnership
                interest at $20 per unit, or $75,000,000. The offering
                terminated on November 30, 1992, at which time 3,513,594 limited
                partnership units had been sold.

        (b)     Leasing Company and Leasing Agent Agreement

                The Partnership 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 and the Leasing Company. 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 XII, 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                                   $1,405,524            $1,601,580
         Less:
         Direct operating payables and accrued expenses               407,473               428,702
         Damage protection reserve                                     85,543               138,819
         Base management fees payable                                 242,422               268,241
         Reimbursed administrative expenses                            60,369                76,784
         Allowance for doubtful accounts                              165,074               171,573
                                                                   ----------            ----------

         Net lease receivables                                     $  444,643            $  517,461
                                                                   ==========            ==========
</TABLE>


                                                                     (Continued)



                                       8
<PAGE>   9

                            IEA INCOME FUND XII, 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 and
        its affiliates 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 were as follows:

<TABLE>
<CAPTION>
                                                      Three Months Ended
                                               --------------------------------
                                                March 31,             March 31,
                                                  2001                  2000
                                               ----------            ----------
<S>                                            <C>                   <C>
Rental revenue (note 4)                        $1,451,896            $1,759,088
Less:
Rental equipment operating expenses               359,532               565,073
Base management fees                              100,426               115,990
Reimbursed administrative expenses                 78,827               123,504
                                               ----------            ----------

                                               $  913,111            $  954,521
                                               ==========            ==========
</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 cargo
        containers. As of March 31, 2001, the Partnership operated 8,747
        twenty-foot, 5,011 forty-foot and 203 forty-foot high-cube marine dry
        cargo containers, as well as 236 twenty-foot and 266 forty-foot marine
        refrigerated cargo containers. A summary of gross lease revenue, by
        product, for the three-month periods ended March 31, 2001 and 2000
        follows:

<TABLE>
<CAPTION>
                                                   Three Months Ended
                                            --------------------------------
                                             March 31,             March 31,
                                               2001                  2000
                                            ----------            ----------
         <S>                                <C>                   <C>
         Dry cargo containers               $1,188,227            $1,422,865
         Refrigerated containers               263,669               336,223
                                            ----------            ----------

         Total                              $1,451,896            $1,759,088
                                            ==========            ==========
</TABLE>

        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 $1,455,856 in cash and cash
        equivalents, an increase of $56,656 from the cash balances at December
        31, 2000. Contributing to this change was the Registrants' efforts to
        increase its working capital reserves. This increase was partially
        offset by the Registrants' results from operations, impacted by a
        declining fleet size and conditions created by the slowdown in the
        global economy.

        The Registrant's operating performance contributed to a 14% decline in
        net lease receivables at March 31, 2001 when compared to December 31,
        2000. The decrease is primarily due to a 12% decrease in gross lease
        receivables, a component of net lease receivables.

        During the first quarter of 2001, distributions from operations and
        sales proceeds amounted to $1,059,933. This represents an increase from
        the $980,878 distributed during the fourth 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.


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
        $913,111, a decline of 4% from the same period in the prior year. Gross
        rental revenue (a component of net lease revenue) for the three-month
        period ended March 31, 2001 was $1,451,896, reflecting a decline of 17%
        from the same period in the prior year. Gross lease revenue was
        primarily impacted by lower per-diem rental rates and a decrease in
        utilization rates. Average dry cargo container per-diem rental rates for
        the three-month period ended March 31, 2001 declined approximately 1%
        when compared to the same period in the prior year. Average refrigerated
        container per-diem rental rates for the three-month period ended March
        31, 2001 declined approximately 4% when compared to the same period in
        the prior year.

        The Registrant's average fleet size and utilization rates for each of
        the three-month periods ended March 31, 2001 and 2000 were as follows:

<TABLE>
<CAPTION>
                                                                    Three Months Ended
                                                               ----------------------------
                                                               March 31,          March 31,
                                                                 2001               2000
                                                               ---------          ---------
         <S>                                                   <C>                <C>
         Average fleet size (measured in twenty-foot
            equivalent units (TEU))
               Dry cargo containers                             19,295             19,938
               Refrigerated containers                             761                775
         Average utilization
               Dry cargo containers                                 69%                74%
               Refrigerated containers                              72%                84%
</TABLE>


                                                                     (Continued)



                                       10
<PAGE>   11

        Rental equipment operating expenses were 25% of the Registrant's gross
        lease revenue during the three-month period ended March 31, 2001, as
        compared to 32% during the three-month period ended March 31, 2000. The
        decrease was primarily due to the $103,679 reduction in the provision
        for doubtful accounts and related expenses, as well as reductions in
        repair and maintenance, and repositioning expenses of $97,721. These
        decreases were partially offset by an increase in storage of $24,993,
        which typically increase with a reduction in utilization. The
        Registrant's operating results contributed to a decline in base
        management fees when compared to the same period in the prior year.

        The Registrant disposed of 141 twenty-foot and 34 forty-foot dry cargo
        containers during the first quarter of 2001, compared to 57 twenty-foot,
        28 forty-foot and one forty-foot high-cube marine dry cargo containers
        during the same period in the prior year. These disposals resulted in a
        loss of $93,287 for the first quarter of 2001, as compared to a loss of
        $40,776 for the same period in the prior year. 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 December
                 2, 1991

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

       10        Form of Leasing Agent Agreement with Cronos                  ***
                 Containers Limited
</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 December 2, 1991, included as part of Registration
        Statement on Form S-1 (No. 33-42697)

**      Incorporated by reference to Exhibit 3.2 to the Registration Statement
        on Form S-1 (No. 33-42697)

***     Incorporated by reference to Exhibit 10.2 to the Registration Statement
        on Form S-1 (No. 33-42697)



                                       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 XII, 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 December
                 2, 1991

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

       10        Form of Leasing Agent Agreement with Cronos                  ***
                 Containers Limited
</TABLE>

----------

*       Incorporated by reference to Exhibit "A" to the Prospectus of the
        Registrant dated December 2, 1991, included as part of Registration
        Statement on Form S-1 (No. 33-42697)

**      Incorporated by reference to Exhibit 3.2 to the Registration Statement
        on Form S-1 (No. 33-42697)

***     Incorporated by reference to Exhibit 10.2 to the Registration Statement
        on Form S-1 (No. 33-42697)