<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D. C. 20549

                                    FORM 10-Q


                   QUARTERLY REPORT UNDER SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934


For quarter ended June 30, 2001

Commission File Number 000 - 25161


                             MODTECH HOLDINGS, INC.
--------------------------------------------------------------------------------


             Delaware                                           33 - 0825386
---------------------------------                            -------------------
  (State or other jurisdiction                                (I.R.S. Employer
of Incorporation or organization)                            Identification No.)


    2830 Barrett Avenue, Perris, CA                                 92571
---------------------------------------                      -------------------
(Address of principal executive office)                          (Zip Code)


                 Registrant's telephone number: (909) 943-4014

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


     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
                                      ---       ---

As of August 9, 2001, there were 13,452,099 of the Registrant's Common Stock
outstanding.

<PAGE>   2

                             MODTECH HOLDINGS, INC.

                                    FORM 10-Q

                       FOR THE QUARTER ENDED JUNE 30, 2001

PART I. STATEMENT REGARDING FINANCIAL INFORMATION

     The condensed consolidated financial statements included herein have been
prepared by Modtech Holdings, Inc. and subsidiaries (the "Company"), without
audit, pursuant to the rules and regulations of the Securities and Exchange
Commission. Certain information normally included in financial statements
prepared in accordance with accounting principles generally accepted in the
United States of America has been omitted pursuant to such rules and
regulations. However, the Company believes that the condensed consolidated
financial statements, including the disclosures herein, are adequate to make the
information presented not misleading. The results of operations for the three
and six months ended June 30, 2001 and 2000 are not necessarily indicative of
the results to be expected for the full fiscal years. The condensed consolidated
financial statements should be read in conjunction with the Company's
consolidated financial statements and notes thereto included in the Company's
Annual Report on Form 10-K for the year ended December 31, 2000 as filed with
the Securities and Exchange Commission.


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<PAGE>   3

                             MODTECH HOLDINGS, INC.

                      Condensed Consolidated Balance Sheets
<TABLE>
<CAPTION>

                                                      December 31,      June 30,
                                                          2000            2001
                                                      ------------    ------------
                                                       (Audited)       (Unaudited)
                                     Assets
<S>                                                   <C>             <C>
Current assets:
  Cash and cash equivalents                           $    416,000    $    851,000
  Contracts receivable, net, including costs
    in excess of billings of $9,724,000 and
    $14,460,000 in 2000 and 2001, respectively          43,813,000      52,313,000
  Inventories                                            9,815,000      11,535,000
  Due from affiliates                                      702,000          11,000
  Deferred tax assets                                    3,407,000       3,407,000
  Other current assets                                   1,010,000       1,341,000
                                                      ------------    ------------
      Total current assets                              59,163,000      69,458,000
                                                      ------------    ------------

Property and equipment, net                             14,538,000      15,676,000

Other assets
    Goodwill, net                                      111,157,000     111,099,000
    Covenants not to compete, net                        1,188,000         820,000
    Debt issuance costs, net                             1,205,000       1,015,000
    Deferred tax assets                                     56,000          56,000
    Other assets                                           395,000         531,000
                                                      ------------    ------------
                                                      $187,702,000    $198,655,000
                                                      ============    ============

                     Liabilities and Shareholders' Equity

Current liabilities:
  Accounts payable and accrued liabilities            $ 23,107,000    $ 21,503,000
  Billings in excess of costs                            4,003,000       3,584,000
  Current revolving credit line                          6,500,000      18,275,000
  Current maturities of long-term debt                   8,400,000       9,000,000
                                                      ------------    ------------
      Total current liabilities                         42,010,000      52,362,000

Long-term debt, excluding current portion               23,600,000      18,800,000
                                                      ------------    ------------
      Total liabilities                                 65,610,000      71,162,000
                                                      ------------    ------------

Shareholders' Equity:
  Series A preferred stock, $.01 par. Authorized
    5,000,000 shares; issued and outstanding
    388,939 in 2000 and 2001                                 4,000           4,000
  Common stock, $.01 par. Authorized 25,000,000
    shares; issued and outstanding 13,348,015 and
    13,452,099 in 2000 and 2001, respectively
                                                           133,000         135,000
  Additional paid-in capital                            78,008,000      78,331,000
  Retained earnings                                     43,947,000      49,023,000
                                                      ------------    ------------
      Total shareholders' equity                       122,092,000     127,493,000
                                                      ------------    ------------
                                                      $187,702,000    $198,655,000
                                                      ============    ============
</TABLE>

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


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<PAGE>   4

                             MODTECH HOLDINGS, INC.

                   Condensed Consolidated Statements of Income

                                   (Unaudited)

<TABLE>
<CAPTION>
                                                         Three Months Ended                    Six Months Ended
                                                              June 30,                             June 30,
                                                   ------------------------------      --------------------------------
                                                       2000              2001              2000                2001
                                                   ------------      ------------      -------------      -------------
<S>                                                <C>               <C>               <C>                <C>
Net sales                                          $ 65,182,000      $ 61,084,000      $ 108,904,000      $ 103,764,000
Cost of goods sold                                   55,463,000        50,059,000         93,363,000         86,667,000
                                                   ------------      ------------      -------------      -------------
        Gross profit                                  9,719,000        11,025,000         15,541,000         17,097,000

Selling, general, and administrative expenses         1,988,000         2,277,000          3,828,000          3,972,000
Goodwill and covenant amortization                      925,000           925,000          1,851,000          1,851,000
                                                   ------------      ------------      -------------      -------------
        Income from operations                        6,806,000         7,823,000          9,862,000         11,274,000
                                                   ------------      ------------      -------------      -------------

Other income (expense):
    Interest expense, net                            (1,210,000)         (837,000)        (2,224,000)        (1,742,000)
    Other, net                                           19,000            33,000             27,000             46,000
                                                   ------------      ------------      -------------      -------------
                                                     (1,191,000)         (804,000)        (2,197,000)        (1,696,000)
                                                   ------------      ------------      -------------      -------------

         Income before income taxes                   5,615,000         7,019,000          7,665,000          9,578,000

Income taxes                                         (2,583,000)       (3,299,000)        (3,526,000)        (4,502,000)
                                                   ------------      ------------      -------------      -------------
         Net income                                $  3,032,000      $  3,720,000      $   4,139,000      $   5,076,000
                                                   ============      ============      =============      =============
Series A Preferred stock dividend                        39,000            39,000             78,000             78,000

          Net income available to common stock     $  2,993,000      $  3,681,000      $   4,061,000      $   4,998,000
                                                   ============      ============      =============      =============

Basic earnings per common share                    $       0.23      $       0.27      $        0.31      $        0.37
                                                   ============      ============      =============      =============

Basic weighted-average shares outstanding            13,196,000        13,387,000         13,176,000         13,369,000
                                                   ============      ============      =============      =============

Diluted earnings per common share                  $       0.21      $       0.26      $        0.29      $        0.36
                                                   ============      ============      =============      =============

Diluted weighted-average shares outstanding          14,399,000        14,517,000         14,332,000         14,374,000
                                                   ============      ============      =============      =============
</TABLE>

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

                                       4

<PAGE>   5

                             MODTECH HOLDINGS, INC.

                 Condensed Consolidated Statements of Cash Flows

                                   (Unaudited)

<TABLE>
<CAPTION>
                                                               Six Months Ended
                                                                   June 30,
                                                         ----------------------------
                                                             2000            2001
                                                         ------------    ------------
<S>                                                      <C>             <C>
Cash flows from operating activities:
  Net income                                             $  4,139,000    $  5,076,000
  Adjustments to reconcile net income to net cash
    used in operating activities:
    Depreciation and amortization                           2,918,000       3,127,000
    Gain on sale of equipment                                      --         (20,000)
    (Increase) decrease in assets, net of effects
      from acquisitions:
      Contracts receivable                                (28,310,000)     (7,974,000)
      Inventories                                          (4,988,000)       (875,000)
      Due from affiliates                                     256,000         691,000
      Other current and noncurrent assets                      56,000        (413,000)
    Increase (decrease) in liabilities, net of
      effects from acquisitions:
      Accounts payable and accrued liabilities             13,957,000      (2,846,000)
      Billings in excess of costs                          (1,571,000)       (419,000)
                                                         ------------    ------------
          Net cash used in operating activities           (13,543,000)     (3,653,000)
                                                         ------------    ------------

Cash flows from investing activities:
  Proceeds from sale of equipment                                  --          25,000
  Purchase of property and equipment                       (1,983,000)       (405,000)
  Purchase of covenants not to compete                             --         (25,000)
  Acquisition of subsidiaries, net of cash acquired                --      (3,406,000)
                                                         ------------    ------------
          Net cash used in investing activities            (1,983,000)     (3,811,000)
                                                         ------------    ------------

Cash flows from financing activities:
  Net principal borrowings under revolving credit line     19,325,000      11,775,000
  Net principal payments on long-term debt                 (3,500,000)     (4,200,000)
  Proceeds from exercise of stock options                     130,000         324,000
                                                         ------------    ------------
          Net cash provided by financing activities        15,955,000       7,899,000
                                                         ------------    ------------

Net increase in cash and cash equivalents                     429,000         435,000

Cash and cash equivalents at beginning of period            1,198,000         416,000
                                                         ------------    ------------
Cash and cash equivalents at end of period               $  1,627,000    $    851,000
                                                         ============    ============
</TABLE>

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

                                       5

<PAGE>   6

                             MODTECH HOLDINGS, INC.

              Notes To Condensed Consolidated Financial Statements

                                   (Unaudited)

                                  June 30, 2001

(1)  Management Opinion

     In the opinion of management, the condensed consolidated financial
     statements reflect all adjustments (which include only normal recurring
     adjustments) necessary to present fairly the financial position and results
     of operations as of and for the periods presented.

     The results of operations for the three and six months ended June 30, 2000
     and 2001 are not necessarily indicative of the results to be expected for
     the full fiscal year.

     Certain statements in this report constitute "forward looking statements"
     within the meaning of Section 27A of the Securities Act of 1933 and Section
     21E of the Securities Exchange Act of 1934. Such forward looking statements
     involve known and unknown risks, uncertainties and other factors which may
     cause the actual results, performance, or achievements of the Company to be
     materially different from any future results, performance, or achievements,
     expressed or implied by such forward looking statements.

(2)  Inventories

     Inventories consist of the following:

                                       2000                 2001
                                    ----------           ----------

     Raw materials                  $8,394,000          $ 8,262,000
     Work in process                 1,413,000            3,265,000
     Finished goods                      8,000                8,000
                                    ----------           ----------
                                    $9,815,000          $11,535,000
                                    ==========          ===========

(3)  Earnings Per Share

     The following table presents the calculation of basic and diluted earnings
     per common share under the provisions of SFAS No. 128:

<TABLE>
<CAPTION>
                                                Three Months Ended                   Six Months Ended
                                                     June 30,                            June 30,
                                           ------------------------------      ------------------------------
                                               2000              2001              2000               2001
                                           ------------      ------------      ------------      ------------
<S>                                        <C>               <C>               <C>               <C>
     BASIC
     Net income                            $  3,032,000      $  3,720,000      $  4,139,000      $  5,076,000
     Dividends on preferred stock               (39,000)          (39,000)          (78,000)          (78,000)
                                           ------------      ------------      ------------      ------------
        Net income available to common
          stock                            $  2,993,000      $  3,681,000      $  4,061,000      $  4,998,000
                                           ============      ============      ============      ============

     Basic weighted-average shares
       outstanding                           13,196,000        13,387,000        13,176,000        13,369,000
                                           ============      ============      ============      ============

     Basic earnings per common share       $       0.23      $       0.27      $       0.31      $       0.37
                                           ============      ============      ============      ============
</TABLE>


                                       6

<PAGE>   7

<TABLE>
<CAPTION>
                                                   Three Months Ended               Six Months Ended
                                                        June 30,                        June 30,
                                               ---------------------------     ---------------------------
                                                  2000            2001            2000            2001
                                               -----------     -----------     -----------     -----------
<S>                                        <C>               <C>               <C>               <C>
     DILUTED
     Net income                                $ 3,032,000     $ 3,720,000     $ 4,139,000     $ 5,076,000
                                               ===========     ===========     ===========     ===========

     Basic weighted-average shares
       outstanding                              13,196,000      13,387,000      13,176,000      13,369,000

     Add:
          Conversion of preferred stock            389,000         389,000         389,000         389,000
          Exercise of stock options                814,000         741,000         767,000         616,000
                                               -----------     -----------     -----------     -----------

     Diluted weighted-average shares
       outstanding                              14,399,000      14,517,000      14,332,000      14,374,000
                                               ===========     ===========     ===========     ===========

     Diluted earnings per common share         $      0.21     $      0.26     $      0.29     $      0.36
                                               ===========     ===========     ===========     ===========
</TABLE>

     Options to purchase 204,000 and 547,000 shares of common stock were
     outstanding during the three and six months ended June 30, 2000,
     respectively, and options to purchase 218,000 and 611,000 shares of common
     stock were outstanding during the three and six months ended June 30, 2001,
     respectively, but were not included in the computation of diluted earnings
     per share because the option exercise price was greater than the average
     market price of the common shares and therefore, the effect would be
     anti-dilutive.

(4)  Acquisition

     IMS Acquisition. On March 8, 2001, the Company purchased 100% of the stock
     of Innovative Modular Structures, Inc. (IMS). IMS designs and manufactures
     modular relocatable classrooms and other modular buildings for commercial
     use. IMS is based in St. Petersburg, Florida. Pro forma amounts for the IMS
     acquisition are not included, as the effect is not material to the
     Company's consolidated financial statements. This acquisition has been
     accounted for as a purchase.


                                       7

<PAGE>   8

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

Results of Operations

The following table sets forth certain items in the Condensed Consolidated
Statements of Income as a percent of net sales.

<TABLE>
<CAPTION>
                                           Percent of Net Sales          Percent of Net Sales
                                           --------------------          --------------------
                                            Three Months Ended             Six Months Ended
                                                 June 30,                      June 30,
                                           --------------------          --------------------
                                           2000           2001           2000           2001
                                           -----          -----          -----          -----
<S>                                        <C>            <C>            <C>            <C>
Net sales                                  100.0%         100.0%         100.0%         100.0%

Gross profit                                14.9           18.0           14.3           16.5

Selling, general and administrative
  expenses                                   3.0            3.7            3.5            3.8

Goodwill and covenant amortization           1.4            1.5            1.7            1.8

Income from operations                      10.4           12.8            9.1           10.9

Interest expense, net                       (1.9)          (1.4)          (2.0)          (1.7)

Income before income taxes                   8.6           11.5            7.0            9.2
</TABLE>

Net sales for the three and six months ended June 30, 2001, decreased by
$4,098,000 or 6.3% and $5,140,000 or 4.7%, respectively. The Company has seen a
shift in product mix from higher volume, lower gross margin standard units
toward a more customized unit. These customized units typically generate higher
margins.

Gross profit as a percentage of net sales for the three and six months ended
June 30, 2001 increased to 18.0% and 16.5%, respectively, from 14.9% and 14.3%
for the same periods in 2000. The increase was due to product mix as well as
certain operational efficiencies.

Selling, general and administrative expenses increased for the three and six
months ended June 30, 2001 by $289,000 or 14.5% and $144,000 or 3.8%,
respectively. As a percentage of net sales, selling, general, and administrative
expenses for the three and six months ended June 30, 2001 are 3.7% and 3.8%,
respectively. The percentages were 3.0% and 3.5% for the same periods in 2000.
Certain additional costs have been incurred in 2001 in the marketing of a new
product for the Florida market.

Goodwill was recorded for both the SPI Merger and the Coastal Acquisition in
1999 and for the IMS acquisition in 2001 and has been amortized from the
respective dates of acquisition.

Interest expense, net decreased for the three and six months ended June 30, 2001
by $373,000 or 30.8% and $482,000 or 21.7%, respectively. The decrease is
attributable to decreased line of credit borrowings, decreased long-term debt
due to repayments and decreased interest rates for the three and six months
ended June 30, 2001. As a percentage of net sales, interest expense decreased
from 1.9% and 2.0% in the three and six months ended June 30, 2000,
respectively, to 1.4% and 1.7% in the three and six months ended June 30, 2001,
respectively.


                                       8


<PAGE>   9

INFLATION

In the past, the Company has not been adversely affected by inflation, because
it has been generally able to pass along to its customers increases in the costs
of labor and materials.

LIQUIDITY AND CAPITAL RESOURCES

To date, the Company has generated cash from operations, bank borrowings and
public offerings to meet its needs. At June 30, 2001, the Company had $851,000
in cash and cash equivalents. During the six months ended June 30, 2001, the
Company used cash from operating activities of $3,653,000.

The Company has a $75,000,000 credit facility, of which $30,000,000 represents a
revolving loan commitment. For the period June 1 through December 31 of each
year, the revolving loan commitment increases to $41,000,000. The credit
facility is secured by all the Company's assets, as well as the Company's stock
ownership in its subsidiaries. The credit facility expires in February 2004. On
June 30, 2001, $18,275,000 was outstanding under the revolving loan commitment,
compared to $19,325,000 outstanding at June 30, 2000. The credit facility
contains various covenants. The Company was in compliance with such covenants as
of June 30, 2001.

Management believes that the Company's existing product lines and manufacturing
capacity will enable the Company to generate sufficient cash through operations,
supplemented by periodic use of its existing bank line of credit, to finance the
Company's business at current levels over the next 12 months. Additional cash
resources may be required if the Company is able to expand its business beyond
current levels. For example, it will be necessary for the Company to construct
or acquire additional manufacturing facilities in order for the Company to
compete effectively in new market areas or states which are beyond a 300 mile
radius from one of its production facilities. The construction or acquisition of
new facilities would require significant additional capital. For these reasons,
among others, the Company may need additional debt or equity financing in the
future. There can be, however, no assurance that the Company will be successful
in obtaining such additional financing, or that any such financing will be
available on terms acceptable to the Company.

NEW ACCOUNTING PRONOUNCEMENTS

In June 1998, the Financial Accounting Standards Board (FASB) issued Statement
of Financial Accounting Standards No. 133, "Accounting for Derivative
Instruments and Hedging Activities" (SFAS 133). SFAS 133, as amended,
establishes accounting and reporting standards for derivative instruments,
derivative instruments embedded in other contracts, and hedging activities. SFAS
133, as amended, is effective for all fiscal quarters of fiscal years beginning
after June 15, 2000. The adoption of SFAS 133, as amended, did not have a
material impact on our consolidated financial position or results of operations.

In July 2001, the FASB issued Statement of Financial Accounting Standards No.
141, "Business Combinations" (SFAS 141), and Statement of Financial Accounting
Standards No. 142, "Goodwill and Other Intangible Assets" (SFAS 142). SFAS 141
requires that all business combinations be accounted for under a single method -
the purchase method. Use of the pooling-of-interests method is no longer
permitted. SFAS 141 requires that the purchase method be used for business
combinations initiated after June 30, 2001. SFAS 142 requires that goodwill no
longer be amortized to earnings, but instead reviewed for impairment. Under SFAS
142, the amortization of goodwill ceases upon adoption of the Statement and is
effective for fiscal years beginning after December 15, 2001, which for calendar
year-end companies, will be January 1, 2002.

The Company has historically amortized its goodwill over its estimated useful
lives. Beginning with the adoption of SFAS 142, the Company will cease
amortizing its goodwill. The Company recorded amortization expense in the amount
of $2,916,000 for the year ended December 31, 2000, $729,000 for the three
months ended June 30, 2001 and $1,458,000 for the six months ended June 30,
2001. To the extent that no impairment charges are recorded upon adoption or
application of SFAS 142, similar amounts of amortization will not be recorded in
future periods.

       Item 3. Quantitative And Qualitative Disclosures About Market Risk

We are exposed to market risks related to fluctuations in interest rates on our
$75 million credit facility. During the three and six months ended June 30,
2001, we did not use interest rate swaps or other types of derivative financial
instruments. The carrying value of the credit facility approximates fair value
as the interest rate is variable and resets frequently. Indebtedness under the
credit facility bears interest at the lower of (1) LIBOR plus additional
interest of between 1.5% and 2.25%, or (2) a rate equal to the greater of (i)
the Federal funds rate plus 0.5% or (ii) the bank's prime rate, plus in either
case an additional interest of between 0.25% to 1.0%. We estimate that the
average amount of debt outstanding under the credit facility for 2001 will be
$50 million. Therefore, a one percentage point increase in interest rates would
result in an increase in interest expense of $500,000 for the year.


                                       9

<PAGE>   10

                           PART II. OTHER INFORMATION


Item 1. Legal Proceedings.

        None

Item 2. Changes in Securities

        None

Item 3. Defaults upon Senior Securities

        None

Item 4. Submission of Matters to a Vote of Security Holders

        None

Item 5. Other Information

        None

Item 6. Exhibits and Reports on Form 8-K

        (a) Exhibits

            None

        (b) Reports on Form 8-K

            None


                                       10

<PAGE>   11

                                   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.


                                            Modtech Holdings, Inc.



Date: August 10, 2001                       by: /s/ Shari L. Walgren
                                                --------------------------------
                                                    Shari L. Walgren
                                                    Chief Financial Officer




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