As filed with the Securities and Exchange Commission on April 2, 2007

Registration No. 333-133755

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-2

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

o           Pre-Effective Amendment No.  

 þ          Post-Effective Amendment No. 4

ALLIED CAPITAL CORPORATION

(Exact Name of Registrant as Specified in Charter)

1919 Pennsylvania Avenue, N.W.

Washington, D.C. 20006-3434

(202) 721-6100

(Address and Telephone Number, including Area Code,

of Principal Executive Offices)

William L. Walton, Chairman and Chief Executive Officer

Allied Capital Corporation

1919 Pennsylvania Avenue, N.W.

Washington, D.C. 20006-3434

(Name and Address of Agent for Service)

Copies of information to:

Approximate Date of Proposed Public Offering:

From time to time after the effective date of the Registration Statement.

      If any securities being registered on this form will be offered on a delayed or continuous basis in reliance on Rule 415 under the Securities Act of 1933, other than securities offered in connection with a dividend reinvestment plan, check the following box.   þ

      This Post-Effective Amendment No. 4 will become effective immediately upon filing pursuant to Rule 462(d) under the Securities Act of 1933, as amended.

EXPLANATORY NOTE

      This Post-Effective Amendment No. 4 to the Registration Statement on Form N-2 (File No. 333-133775) of Allied Capital Corporation (the “Registration Statement”) is being filed pursuant to Rule 462(d) under the Securities Act of 1933, as amended (the “Securities Act”), solely for the purpose of filing exhibits to the Registration Statement. Accordingly, this Post-Effective Amendment No. 4 consists only of a facing page, this explanatory note and Part C of the Registration Statement on Form N-2 setting forth the exhibits to the Registration Statement. This Post-Effective Amendment No. 4 does not modify any other part of the Registration Statement. Pursuant to Rule 462(d) under the Securities Act, this Post-Effective Amendment No. 4 shall become effective immediately upon filing with the Securities and Exchange Commission. The contents of the Registration Statement are hereby incorporated by reference.

PART C

OTHER INFORMATION

Item 25. Financial Statements and Exhibits

      1. Financial Statements.

      The following financial statements of Allied Capital Corporation are included in this registration statement in “Part A: Information Required in a Prospectus”:

      2. Exhibits

*     Filed herewith.

Item 26. Marketing Arrangements

      The information contained under the heading “Plan of Distribution” of the prospectus is incorporated herein by reference.

Item 27. Other Expenses of Issuance and Distribution*

*     Estimated for filing purposes and excludes fees previously paid.

     All of the expenses set forth above shall be borne by us.

Item 28. Persons Controlled by or Under Common Control

Direct Subsidiaries

      The following list sets forth each of our subsidiaries, the state or country under whose laws the subsidiary is organized, and the percentage of voting securities or membership interests owned by us in such subsidiary:

      Each of our subsidiaries is consolidated for financial reporting purposes, except as noted below.

Indirect Subsidiaries

      We indirectly control the entities set forth below through Allied REIT. Allied REIT owns either all of the membership interests (in the case of a limited liability company, “LLC”) or all of the outstanding voting stock (in the case of a corporation) of each entity. The following list sets forth each of Allied REIT’s subsidiaries, the state under

whose laws the subsidiary is organized, and the percentage of voting securities or membership interests owned by Allied REIT of such subsidiary:

      We indirectly control Allied Investment Holdings LLC (Delaware) through Allied Investments L.P., which owns 100% of the membership interests. We indirectly control Allied Capital Investors, LLC (Delaware) through A.C. Corporation, which is the sole member and manager. We indirectly control A.C. Management Services, LLC (Delaware) and AC Finance LLC (Delaware) through A.C. Corporation, which is the sole member and manager.

Other Entities Deemed to be Controlled by the Company

We have also established certain limited purpose entities in order to facilitate certain portfolio transactions. In addition, we may be deemed to control certain portfolio companies. See “Portfolio Companies” in the prospectus.

Item 29. Number of Holders of Securities

      The following table sets forth the approximate number of record holders of our common stock at June 6, 2006.

      At June 6, 2006, we have privately issued long-term debt securities to approximately 40 institutional lenders, primarily insurance companies.

Item 30. Indemnification

      Section 2-418 of the Maryland General Corporation Law provides that a Maryland corporation may indemnify any director of the corporation and any person who, while a director of the corporation, is or was serving at the request of the corporation as a director, officer, partner, trustee, employee, or agent of another foreign or domestic corporation, partnership, joint venture, trust, other enterprise or employee benefit plan, made a party to any proceeding by reason of service in that capacity unless it is established that the act or omission of the director was material to the matter giving rise to the proceeding and was committed in bad faith or was the result of active and deliberate dishonesty; or the director actually received an improper personal benefit in money, property or services; or, in the case of any criminal proceeding, the director had reasonable cause to believe that the act or omission was unlawful. Indemnification may be made against judgments, penalties, fines, settlements, and reasonable expenses actually incurred by the director in connection with the proceeding, but if the proceeding was one by or in the right of the corporation, indemnification may not be made in respect of any proceeding in which the director shall have been adjudged to be liable to the corporation. Such indemnification may not be made unless authorized for a specific proceeding after a determination has been made, in the manner prescribed by the law, that indemnification is permissible in the circumstances because the director has met the applicable standard of conduct. On the other hand, the director must be indemnified for expenses if he or she has been successful in the defense of the proceeding or as otherwise ordered by a court. The law also prescribes the

circumstances under which the corporation may advance expenses to, or obtain insurance or similar cover for, directors.

      The law also provides for comparable indemnification for corporate officers and agents.

      The Restated Articles of Incorporation of Allied Capital provide that its directors and officers shall, and its agents in the discretion of the board of directors may be indemnified to the fullest extent permitted from time to time by the laws of Maryland (with such power to indemnify officers and directors limited to the scope provided for in Section 2-418 as currently in force), provided, however, that such indemnification is limited by the Investment Company Act of 1940 or by any valid rule, regulation or order of the Securities and Exchange Commission thereunder. Allied Capital’s bylaws, however, provide that Allied Capital may not indemnify any director or officer against liability to Allied Capital or its security holders to which he or she might otherwise be subject by reason of such person’s willful misfeasance, bad faith, gross negligence or reckless disregard of the duties involved in the conduct of his or her office unless a determination is made by final decision of a court, by vote of a majority of a quorum of directors who are disinterested, non-party directors or by independent legal counsel that the liability for which indemnification is sought did not arise out of such disabling conduct.

      Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of Allied Capital pursuant to the provisions described above, or otherwise, Allied Capital has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by Allied Capital of expenses incurred or paid by a director, officer or controlling person in the successful defense of an action, suit or proceeding) is asserted by a director, officer or controlling person in connection with the securities being registered, Allied Capital will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

      Allied Capital carries liability insurance for the benefit of its directors and officers on a claims-made basis of up to $50,000,000, subject to a $1,000,000 retention and the other terms thereof. Allied Capital also maintains an additional $20,000,000 of insurance coverage for the benefit of its directors and officers.

      We have entered into indemnification agreements with our directors and certain senior officers. The indemnification agreements attempt to provide these directors and senior officers the maximum indemnification permitted under Maryland law and the Investment Company Act of 1940. Each indemnification agreement provides that Allied Capital shall indemnify the director or senior officer who is a party to the agreement (an “Indemnitee”) if, by reason of his corporate status, the Indemnitee is, or is threatened to be, made a party to or a witness in any threatened, pending, or completed proceeding, other than a proceeding by or in the right of Allied Capital.

      At present, these is no pending litigation or proceeding involving an Indemnitee where indemnification would be required or permitted under the indemnification agreement.

Item 31. Business and Other Connections of Investment Adviser

      Not applicable.

Item 32. Location of Accounts and Records

      We maintain at our principal office physical possession of each account, book or other document required to be maintained by Section 31(a) of the 1940 Act and the rules thereunder.

Item 33. Management Services

      Not applicable.

Item 34. Undertakings

      We hereby undertake:

SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Post-Effective Amendment No. 4 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Washington, in the District of Columbia, on the 2nd day of April, 2007.

      Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 4 to the Registration Statement has been signed by the following persons in the capacities indicated on April 2, 2007.

INDEX TO EXHIBITS