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UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

(Mark one)

For the quarterly period ended March 31, 2012

OR

For the transition period from              to             

Commission file no. 0-16851

DEL TACO RESTAURANT PROPERTIES III

(A California limited partnership)

(Exact name of registrant as specified in its charter)

(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  þ        No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  þ        No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨        No  þ

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s Form S-11 Registration Statement filed December 17, 1982 are incorporated by reference into Part IV of this report.

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INDEX

DEL TACO RESTAURANT PROPERTIES III

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PART I.    FINANCIAL INFORMATION

ITEM I.    FINANCIAL STATEMENTS

DEL TACO RESTAURANT PROPERTIES III

CONDENSED BALANCE SHEETS

See accompanying notes to condensed financial statements.

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DEL TACO RESTAURANT PROPERTIES III

CONDENSED STATEMENTS OF INCOME

(Unaudited)

See accompanying notes to condensed financial statements.

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DEL TACO RESTAURANT PROPERTIES III

CONDENSED STATEMENTS OF CASH FLOWS

(Unaudited)

See accompanying notes to condensed financial statements.

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DEL TACO RESTAURANT PROPERTIES III

NOTES TO CONDENSED FINANCIAL STATEMENTS

FOR THE THREE MONTHS ENDED MARCH 31, 2012

UNAUDITED

NOTE 1 – BASIS OF PRESENTATION

The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America 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 accounting principles generally accepted in the United States of America for complete financial statements and should therefore be read in conjunction with the financial statements and notes thereto contained in the annual report on Form 10-K for the year ended December 31, 2011 for Del Taco Restaurant Properties III (the Partnership or the Company). In the opinion of management, all adjustments (consisting of normal recurring accruals) necessary to present fairly the Partnership’s financial position at March 31, 2012, the results of operations for the three month periods ended March 31, 2012 and 2011 and cash flows for the three month periods ended March 31, 2012 and 2011 have been included. Operating results for the three months ended March 31, 2012 are not necessarily indicative of the results that may be expected for the year ending December 31, 2012. Amounts related to disclosure of December 31, 2011 balances within these condensed financial statements were derived from the 2011 audited financial statements.

Management has evaluated events subsequent to March 31, 2012 through the date that the accompanying condensed financial statements were filed with the Securities and Exchange Commission for transactions and other events which may require adjustment of and/or disclosure in such financial statements.

NOTE 2 – RESTRICTED CASH

At March 31, 2012 and December 31, 2011, the Partnership had a restricted cash balance of $86,017. The restricted cash results from a death and disability fund that the Company is required to maintain under the terms of the Partnership agreement. Such fund is maintained in an interest bearing account at a major commercial bank. A limited partner has the right, under certain circumstances involving such limited partner’s death or disability, to tender to the Partnership for redemption all of the units owned of record by such limited partner. The redemption price will be equal to the partners capital account balance as of the redemption date. The death and disability fund was established in 1987. The fund was limited to two percent of the gross proceeds from sale of the limited partnership units. Requests for redemption made after the funds in the death and disability fund are depleted will not be accepted.

NOTE 3 – NET INCOME PER LIMITED PARTNERSHIP UNIT

Net income per limited partnership unit is based on net income attributable to the limited partners (after 1% allocation to the general partner) using the weighted average number of units outstanding during the periods presented which amounted to 47,261 in 2012 and 2011.

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DEL TACO RESTAURANT PROPERTIES III

NOTES TO CONDENSED FINANCIAL STATEMENTS – CONTINUED

FOR THE THREE MONTHS ENDED MARCH 31, 2012

UNAUDITED

NOTE 3 – NET INCOME PER LIMITED PARTNERSHIP UNIT – Continued

Pursuant to the partnership agreement, annual partnership income or loss is allocated one percent to Del Taco LLC, formerly known as Del Taco, Inc. (Del Taco or 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, distributions and syndication costs, and until each class of limited partners receive their priority return as defined in the partnership agreement. Additional gains will be allocated 15 percent to the General Partner and 85 percent to the limited partners.

NOTE 4 – LEASING ACTIVITIES

The Partnership leases certain properties for operation of restaurants to Del Taco 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. The leases expire in the years 2022 to 2024. Pursuant to the lease agreements, minimum rentals of $3,500 per month are due to the Partnership during the first six months of any non-operating period caused by an insured casualty loss.

For the three months ended March 31, 2012, the restaurants operated by Del Taco, for which the Partnership is the lessor, had combined, unaudited sales of $1,969,125 and unaudited net losses of $21,373 as compared to unaudited sales of $2,086,979 and unaudited net losses of $25,010, respectively, for the corresponding period in 2011. Net income or loss of each restaurant includes charges for general and administrative expenses incurred in connection with supervision of restaurant operations and interest expense and the decrease in net loss from the corresponding period of the prior year primarily relates to decreases in operating costs.

NOTE 5 – TRANSACTIONS WITH DEL TACO

The receivable from Del Taco consists primarily of rent accrued for the month of March 2012. The March rent receivable was collected in April 2012.

Del Taco 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 for operation under the Del Taco trade name.

In addition, see Note 6 with respect to certain distributions to the General Partner.

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DEL TACO RESTAURANT PROPERTIES III

NOTES TO CONDENSED FINANCIAL STATEMENTS – CONTINUED

FOR THE THREE MONTHS ENDED MARCH 31, 2012

UNAUDITED

NOTE 6 – DISTRIBUTIONS

Total cash distributions declared and paid in February 2012 were $173,685. On April 27, 2012, a distribution to the limited partners of $210,058, or approximately $4.44 per limited partnership unit, was approved. Such distribution was paid on May 14, 2012. The General Partner also received a distribution of $2,122 with respect to its 1% partnership interest in May 2012.

NOTE 7 – PAYABLE TO LIMITED PARTNERS

Payable to limited partners represents a reclassification from cash for distribution checks made to limited partners that have remained outstanding for six months or longer.

NOTE 8 – CONCENTRATION OF RISK

The restaurants leased to Del Taco make up all of the income producing assets of the Partnership and contributed all of the Partnership’s rental revenues during the three months ended March 31, 2012 and 2011. Therefore, the business of the Partnership is entirely dependent on the success of the Del Taco trade name restaurants that lease the properties.

The Partnership maintains substantially all of its cash and cash equivalents at one major commercial bank. Although the Partnership at times maintains balances that exceed the federally insured limit, it has not experienced any losses related to these balances and management believes the credit risk to be minimal.

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Liquidity and Capital Resources

Del Taco Restaurant Properties III (the Partnership or the Company) offered limited partnership units for sale between February 1986 and June 1987. $12 million was raised through the sale of limited partnership units and used to acquire sites and build ten restaurants and also to pay commissions to brokers and to reimburse Del Taco LLC (the General Partner or Del Taco) for offering costs incurred. In February of 1992, approximately $281,000 raised during the offering but not required to acquire sites and build restaurants was distributed to the limited partners. One restaurant was sold in November 1997.

The restaurants leased to Del Taco make up all of the income producing assets of the Partnership. Therefore, the business of the Partnership is 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, competition, consumer demand and preference for fast food, in general, and for Mexican-American food in particular.

As described in Note 2 to the Notes to the Financial Statements, the Partnership has a death and disability redemption fund totaling $86,017 at March 31, 2012. Investors should contact the General Partner with all questions regarding the eligibility of a limited partner or the estate of a deceased limited partner to participate in the redemption fund.

Results of Operations

The Partnership owns eight properties that are under long-term lease to Del Taco for restaurant operations.

The following table sets forth rental revenue earned by restaurant (unaudited):

The Partnership receives rental revenues equal to 12 percent of gross sales from the restaurants. The Partnership earned rental revenue of $236,295 during the three month period ended March 31, 2012, which represents a decrease of $14,142 from the corresponding period in 2011. The changes in rental revenues between 2011 and 2012 are directly attributable to changes in sales levels at the restaurants under lease due to local competitive and industry factors and the loss of the Plaza at Puente Hills restaurant in the City of Industry. The City of Industry restaurant was destroyed in a fire resulting from an automobile accident during the second quarter of 2011, and the property was subsequently sold in the fourth quarter of 2011.

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

General and administrative costs increased from 2011 to 2012 primarily due to increased costs for printing and legal expenses. Depreciation expense decreased from 2011 to 2012 because certain assets were disposed in relation to the loss at the restaurant in the City of Industry.

For the three month period ended March 31, 2012, net income decreased by $13,433 from 2011 to 2012 due to the decrease in revenues of $14,142 and the increase in general and administrative expenses of $2,590, partially offset by the decrease in depreciation expense of $3,004 and the increase in interest and other income of $295.

Significant Recent Accounting Pronouncements

None.

Off-Balance Sheet Arrangements

None

Critical Accounting Policies and Estimates

Management’s discussion and analysis of financial condition and results of operations, as well as disclosures included elsewhere in this report on Form 10-Q are based upon the Partnership’s financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States of America. The preparation of these financial statements requires management to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses. The Partnership believes the critical accounting policies that most impact the financial statements are described below. A summary of the significant accounting policies of the Partnership can be found in Note 1 to the Financial Statements which is included in the Partnership’s December 31, 2011 Form 10-K.

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Revenue Recognition: Rental revenue is recognized based on 12 percent of gross sales of the restaurants for the corresponding period, and is earned at the point of sale.

Property and Equipment: Property and equipment is stated at cost. Depreciation is computed using the straight-line method over estimated useful lives which are 20 years for land improvements, 35 years for buildings and improvements, and 10 years for machinery and equipment.

The Partnership accounts for property and equipment in accordance with authoritative guidance issued by the Financial Accounting Standards Board that requires long-lived assets be reviewed for impairment whenever events or changes in circumstances indicate that the carrying value of the asset may not be recoverable. In evaluating long-lived assets held for use, an impairment loss is recognized if the sum of the expected future cash flows (undiscounted and without interest charges) is less than the carrying value of the asset. Once a determination has been made that an impairment loss should be recognized for long-lived assets, various assumptions and estimates are used to determine fair value including, among others, estimated costs of construction and development, recent sales of comparable properties and the opinions of fair value prepared by independent real estate appraisers. Long-lived assets to be disposed of are reported at the lower of carrying amount or fair value less cost to sell.

None.

As of the end of the period covered by this quarterly report, we carried out an evaluation, under the supervision and with the participation of the Company’s management, including the Company’s Chief Executive Officer and Chief Financial Officer, of the effectiveness of the design and operation of the Company’s disclosure controls and procedures. Based upon that evaluation, the Chief Executive Officer and Chief Financial Officer concluded that the Company’s disclosure controls and procedures are effective in timely alerting them to material information relating to the Company required to be included in the Company’s periodic Securities and Exchange Commission filings.

There were no significant changes in the Company’s internal controls over financial reporting that occurred during our most recent fiscal quarter that materially affected, or is reasonably likely to materially affect, our internal control over financial reporting.

Not applicable.

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PART III.    OTHER INFORMATION

There is no information required to be reported for any items under Part III, except as follows:

Item 6. Exhibits

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

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