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                                 UNITED STATES

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   FORM 10-Q

(MARK ONE)

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

FOR THE QUARTERLY PERIOD ENDED                  JUNE 30, 2000                  .

                                       OR

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

FOR THE TRANSITION PERIOD FROM  _____________________ TO
 _____________________  .

COMMISSION FILE NO. 2-80930

                        DEL TACO RESTAURANT PROPERTIES I
                        A CALIFORNIA LIMITED PARTNERSHIP
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

<TABLE>
<S>                                                     <C>
                      CALIFORNIA                                  95-3852699
            (STATE OR OTHER JURISDICTION OF                    (I.R.S. EMPLOYER
            INCORPORATION OR ORGANIZATION)                  IDENTIFICATION NUMBER)

 23041 AVENIDA DE LA CARLOTA, LAGUNA HILLS, CALIFORNIA              92653
       (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                   (ZIP CODE)
</TABLE>

                                 (949) 462-9300
              (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  ___

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                                      INDEX

                        DEL TACO RESTAURANT PROPERTIES I



                                                                     PAGE NUMBER
                                                                     -----------
PART I.  FINANCIAL INFORMATION PAGE NUMBER

Item 1.  Financial Statements and Supplementary Data

         Balance Sheets at June 30, 2000 (Unaudited) and
         December 31, 1999                                                3

         Statements of Income for the three and six months ended
         June 30, 2000 and 1999 (Unaudited)                               4

         Statements of Cash Flows for the six months ended
         June 30, 2000 and 1999 (Unaudited)                               5

         Notes to Financial Statements                                    6

Item 2.  Management's Discussion and Analysis of
         Financial Condition and Results of Operations                    8

PART II. OTHER INFORMATION

Item 6.  Exhibits and Reports on Form 8-K                                10

SIGNATURES                                                               11


                                      -2-
<PAGE>   3

                        DEL TACO RESTAURANT PROPERTIES I

                                 BALANCE SHEETS

                                           June 30,      December 31,
                                             2000            1999
                                         ------------     ----------
                                         (Unaudited)

                               ASSETS
CURRENT ASSETS:
     Cash                                 $  167,341      $  170,290
     Receivable from General Partner          51,434          46,970
     Deposits                                    600             600
                                          ----------      ----------
         Total current assets                219,375         217,860
                                          ----------      ----------
PROPERTY AND EQUIPMENT, at cost:
     Land and improvements                 1,852,482       1,852,482
     Buildings and improvements            1,013,134       1,013,134
     Machinery and equipment               1,136,026       1,136,026
                                          ----------      ----------
                                           4,001,642       4,001,642
     Less--accumulated depreciation        1,781,745       1,759,859
                                          ----------      ----------
                                           2,219,897       2,241,783
                                          ----------      ----------
                                          $2,439,272      $2,459,643
                                          ==========      ==========

                 LIABILITIES AND PARTNERS' EQUITY

CURRENT LIABILITIES:
     Payable to Limited Partners          $   38,752      $   31,001
     Accounts payable                          4,929           7,828
                                          ----------      ----------
         Total current liabilities            43,681          38,829
                                          ----------      ----------
PARTNERS' EQUITY:
     Limited Partners                      2,131,538       2,156,509
     General Partner-Del Taco, Inc.          264,053         264,305
                                          ----------      ----------
                                           2,395,591       2,420,814
                                          ----------      ----------
                                          $2,439,272      $2,459,643
                                          ==========      ==========

                          The accompanying notes are an
                   integral part of these financial statements

                                       -3-

<PAGE>   4

                        DEL TACO RESTAURANT PROPERTIES I

                              STATEMENTS OF INCOME

                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                       Three Months Ended           Six Months Ended
                                            June 30,                    June 30,
                                     ----------------------      ----------------------
                                       2000          1999          2000          1999
                                     --------      --------      --------      --------
<S>                                  <C>           <C>           <C>           <C>
REVENUES:
     Rent                            $144,883      $130,880      $279,134      $256,537
     Interest                           1,489           925         2,367         2,082
     Other                                 75           175           375           600
                                     --------      --------      --------      --------
                                      146,447       131,980       281,876       259,219
                                     --------      --------      --------      --------
EXPENSES:
     General and administrative         9,621         9,935        30,875        31,026
     Depreciation                      10,943        10,943        21,886        21,886
                                     --------      --------      --------      --------
                                       20,564        20,878        52,761        52,912
                                     --------      --------      --------      --------
         Net income                  $125,883      $111,102      $229,115      $206,307
                                     ========      ========      ========      ========
     Net income per limited
        partnership unit             $  14.24      $  12.57      $  25.92      $  23.34
                                     ========      ========      ========      ========
</TABLE>

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

                                       -4-

<PAGE>   5

                        DEL TACO RESTAURANT PROPERTIES I

                            STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                                 Six Months Ended
                                                                      June 30,
                                                              -----------------------
                                                                2000           1999
                                                              ---------     ---------
<S>                                                           <C>           <C>
CASH FLOWS FROM OPERATING ACTIVITIES:

Net income                                                    $ 229,115     $ 206,307
Adjustments to reconcile net income to net
  cash provided by operating activities:
     Depreciation                                                21,886        21,886
     (Increase) decrease in receivable from General Partner      (4,463)        3,234
     Decrease in deposits                                            --            30
     Increase in accounts payable and payable
        to limited partners                                       4,851         2,085
                                                              ---------     ---------
             Net cash provided by operating activities          251,389       233,542

CASH FLOWS FROM FINANCING ACTIVITIES:

Cash distributions to partners                                 (254,338)     (247,447)
                                                              ---------     ---------
Net decrease in cash                                             (2,949)      (13,905)

Beginning cash balance                                          170,290       162,979
                                                              ---------     ---------
Ending cash balance                                           $ 167,341     $ 149,074
                                                              =========     =========
</TABLE>

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

                                       -5-

<PAGE>   6

                        DEL TACO RESTAURANT PROPERTIES I

                          NOTES TO FINANCIAL STATEMENTS

                                  JUNE 30, 2000


NOTE 1 - BASIS OF PRESENTATION

The accompanying financial statements, some of which are unaudited, have been
prepared in accordance with generally accepted accounting principles for interim
financial information and with the instructions to Form 10-Q and Article 10 of
Regulation S-X. Accordingly, they do not include all of the information and
footnotes required by generally accepted accounting principles for complete
financial statements and should therefore be read in conjunction with the
financial statements and notes thereto contained in the Registrant's annual
report on Form 10-K for the year ended December 31, 1999. In the opinion of
management, all adjustments (consisting of normal recurring accruals) necessary
to present fairly the partnership's financial position at June 30, 2000, the
results of operations and cash flows for the six month periods ended June 30,
2000 and 1999 have been included. Operating results for the three and six months
ended June 30, 2000 are not necessarily indicative of the results that may be
expected for the year ending December 31, 2000.

NOTE 2 - NET INCOME PER LIMITED PARTNERSHIP UNIT

Net income per limited partnership unit is based upon the weighted average
number of units outstanding during the periods presented, which amounted to
8,751 in 2000 and 1999.

Pursuant to the partnership agreement, annual partnership net income is
allocated one percent to the General Partner and 99 percent to the limited
partners. A partnership net loss in any year will be allocated 24 percent to the
General Partner and 76 percent to the limited partners until the losses so
allocated equal income previously allocated. Any additional losses will be
allocated one percent to the General Partner and 99 percent to the limited
partners. Partnership gains from any sale or refinancing will be allocated one
percent to the General Partner and 99 percent to the limited partners until
allocated gains and profits equal losses. Additional gains will be allocated 24
percent to the General Partner and 76 percent to the limited partners.

NOTE 3 - LEASING ACTIVITIES

The partnership leases certain properties for operation of restaurants to Del
Taco, Inc. on a triple net basis. The leases are for terms of 35 years
commencing with the completion of the restaurant facility located on each
property and require monthly rentals equal to 12 percent of the gross sales of
the restaurants. There is no minimum rental under any of the leases.


                                       -6-

<PAGE>   7

                        DEL TACO RESTAURANT PROPERTIES I

                    NOTES TO FINANCIAL STATEMENTS - CONTINUED

                                  JUNE 30, 2000

NOTE 3 - LEASING ACTIVITIES - CONTINUED

For the three months ended June 30, 2000, the five restaurants operated by Del
Taco, for which the partnership is the lessor, had combined, unaudited sales of
$1,005,834 and net income of $61,342 as compared to $905,803 and $46,489
respectively, for the corresponding period in 1999. Net income by restaurant
includes charges for general and administrative expenses incurred in connection
with supervision of restaurant operations and interest expense (1999 combined,
unaudited net income amounts have been changed to measure net income on a
consistent basis with the year 2000 presentation). For the three months ended
June 30, 2000, the one restaurant operated by a Del Taco franchisee, for which
the partnership is the lessor, had unaudited sales of $201,525 as compared with
$184,867 during the same period in 1999.

For the six months ended June 30, 2000, the five restaurants operated by Del
Taco, for which the partnership is the lessor, had combined, unaudited sales of
$1,933,897 and net income of $105,100 as compared to $1,779,012 and $78,688
respectively, for the corresponding period in 1999. For the six months ended
June 30, 2000, the one restaurant operated by a Del Taco franchisee, for which
the partnership is the lessor, had unaudited sales of $392,223 as compared with
$358,800 during the same period in 1999.

For the three months and six months ended June 30, 2000, the Elkhorn Boulevard
restaurant in Sacramento, California reported net income of $629 and a net loss
of $3,187 as compared to net losses of $1,058 and $4,941 for the corresponding
periods in 1999.

NOTE 4 - TRANSACTIONS WITH DEL TACO

The receivable from General Partner consists primarily of rent accrued for the
month of June. The June rent receivable was collected on July 13, 2000.

Del Taco, Inc. serves in the capacity of general partner in other partnerships
which are engaged in the business of operating restaurants, and three other
partnerships which were formed for the purpose of acquiring real property in
California for construction of Mexican-American restaurants for lease under
long-term agreements to Del Taco, Inc. for operation under the Del Taco trade
name.

In addition, see Note 5 with respect to certain distributions to the General
Partner.

NOTE 5 - DISTRIBUTIONS

On July 17, 2000, a distribution to the limited partners of $122,354, or
approximately $13.98 per limited partnership unit, was approved. Such
distribution was paid on July 18, 2000. The General Partner also received a
distribution of $1,236 with respect to its 1% partnership interest.


                                       -7-

<PAGE>   8

ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
        RESULTS OF OPERATIONS

Liquidity and Capital Resources

The partnership offered limited partnership units for sale between March 1983
and March 1984. 15% of the $4.375 million raised through sale of limited
partnership units was used to pay commissions to brokers and to reimburse the
General Partner for offering costs incurred. Approximately $4 million of the
remaining funds were used to acquire sites and build six restaurants.

The six restaurants leased to Del Taco make up almost all of the income
producing assets of the partnership. Therefore, the business of the partnership
is almost entirely dependent on the success of the Del Taco trade name
restaurants that lease the properties. The success of the restaurants is
dependent on a large variety of factors, including, but not limited to, consumer
demand and preference for fast food, in general, and for Mexican-American food
in particular.

Results of Operations

The partnership owns six properties that are under long-term lease to Del Taco
for restaurant operations (Del Taco, in turn, has subleased two of the
restaurants to Del Taco franchisees, one of which is affiliated with Del Taco).

The following table sets forth rental revenue earned by restaurant for the year:

<TABLE>
<CAPTION>
                                               THREE MONTHS ENDED       SIX MONTHS ENDED
                                                    JUNE 30,                JUNE 30,
                                              --------------------    --------------------
                                                2000        1999        2000        1999
                                              --------    --------    --------    --------
<S>                                           <C>         <C>         <C>         <C>
Riverside Avenue, Rialto, CA                  $ 22,228    $ 21,295    $ 43,455    $ 41,452

Elden Avenue, Moreno Valley, CA                 24,184      19,695      46,169      38,807

Foothill Boulevard, La Verne, CA                30,639      28,598      58,115      55,461

Baseline & Archibald, Rancho Cucamonga, CA      24,183      22,184      47,067      43,056

Elkhorn Boulevard, Sacramento, CA               15,843      15,070      30,222      28,907

Haven Avenue, Rancho Cucamonga, CA              27,806      24,038      54,106      48,854
                                              --------    --------    --------    --------
         Total                                $144,883    $130,880    $279,134    $256,537
                                              ========    ========    ========    ========
</TABLE>

The partnership receives rental revenues equal to 12 percent of gross sales from
the restaurants. The partnership earned rental revenue of $144,883 during the
three month period ended June 30, 2000, which represents an increase of $14,003
from 1999. The partnership earned rental revenue of $279,134 during the six
month period ended June 30, 2000, which represents an increase of $22,597 from
1999. The changes in rental revenue between 1999 and 2000 are directly
attributable to changes in sales levels at the restaurants under lease.


                                      -8-

<PAGE>   9

ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
        RESULTS OF OPERATIONS - CONTINUED

The following table breaks down general and administrative expenses by type of
expense:

                               Percentage of Total
                        General & Administrative Expense

                                                            Six Months Ended
                                                                June 30,
                                                          -------------------
                                                           2000         1999
                                                          ------       ------

        Accounting fees                                    65.58%       67.68%
        Distribution of information to Limited Partners    34.42        32.32
                                                          ------       ------
                                                          100.00%      100.00%
                                                          =======      ======

General and administrative costs for the six month period ended June 30,
decreased from 1999 to 2000 due to decreased costs for the distribution of
information to limited partners.

For the three month period ended June 30, 2000, net income increased $14,781
from 1999 to 2000 due to the increase in revenues of $14,467 and a $314 decrease
in general and administrative expenses. For the six month period ended June 30,
2000, net income increased by $22,808 from 1999 to 2000 due to the increase in
revenues of $22,657 and the decrease in general and administrative expenses of
$151.


                                      -9-

<PAGE>   10

PART II. OTHER INFORMATION

Item 6.  Exhibits and Reports on Form 8-K

         (b) No reports on Form 8-K were filed during the six months ended
             June 30, 2000.


                                      -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.


                                            DEL TACO RESTAURANT PROPERTIES I
                                            (a California limited partnership)
                                            Registrant

                                            Del Taco, Inc.
                                            General Partner



Date: July 31, 2000                         /s/ Robert J. Terrano
                                            --------------------------------
                                                Robert J. Terrano
                                                Executive Vice President,
                                                Chief Financial Officer


Date: July 31, 2000                         /s/ C. Douglas Mitchell
                                            --------------------------------
                                                C. Douglas Mitchell
                                                Vice President and Corporate
                                                Controller


                                      -11-
<PAGE>   12


                                 EXHIBIT INDEX

Exhibit
Number                     Description
------                     -----------

 27.1               Financial Data Schedule