The information in this prospectus supplement is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus supplement is not an offer to sell these securities and is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Filed Pursuant to Rule 497

Registration Statement No.            

PROSPECTUS SUPPLEMENT

(To Prospectus dated                    , 201     )

Shares

% Series [            ] Preferred Stock

Liquidation Preference $            per share

We are offering for sale shares of our Series Preferred Stock. Our common stock is traded on The Nasdaq Global Select Market under the symbol “GAIN.” The last reported sale price for our common stock on            , was $            per share. The net asset value per share of our common stock at the close of business on , 201 was $ per share. There currently is no market for the preferred stock. We applied to list the preferred stock on [            ]. The expected trading symbol for the preferred stock is [            ].

The Underwriters are expected to deliver the Series Preferred Stock in book-entry form through the Depositary Trust Company on or about            .

You should read this prospectus supplement and the accompanying prospectus before deciding whether to invest in our preferred stock and you should retain them for future reference. Additional information about us, including our annual, quarterly and current reports, has been filed with the Securities and Exchange Commission. This information is available free of charge on our corporate website at http://www.gladstoneinvestment.com.

An investment in our preferred stock involves certain risks, including, among other things, risks relating to investments in securities of small, private and developing businesses. We describe some of these risks in the section entitled “Risk Factors,” which begins on page P-4 of this prospectus supplement and page 9 of the accompanying prospectus. Shares of closed-end investment companies frequently trade at a discount to their net asset value per share. If our shares trade at a discount to their net asset value, this will likely increase the risk of loss to purchasers of our preferred stock. You should carefully consider these risks together with all of the other information contained in this prospectus supplement and the accompanying prospectus before making a decision to purchase our preferred stock.

The preferred stock being offered has not been approved or disapproved by the Securities and Exchange Commission or any state securities commission nor has the Securities and Exchange Commission or any state securities commission passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

                    , 201

P-1

We have not authorized any dealer, salesman or other person to give any information or to make any representation other than those contained in this prospectus supplement or the accompanying prospectus. You must not rely upon any information or representation not contained in this prospectus supplement or the accompanying prospectus as if we had authorized it. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell or a solicitation of any offer to buy any security other than the registered securities to which they relate, nor do they constitute an offer to sell or a solicitation of an offer to buy any securities in any jurisdiction to any person to whom it is unlawful to make such an offer or solicitation in such jurisdiction. The information contained in this prospectus supplement and any accompanying prospectus is accurate as of the dates on their respective covers only. Our business, financial condition, results of operations and prospects may have changed since such dates.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

P-2

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

All statements contained or incorporated by reference in this prospectus supplement or the accompanying prospectus, other than historical facts, may constitute “forward-looking statements.” These statements may relate to, among other things, future events or our future operating results, our business prospects and the prospects of our portfolio companies, actual and potential conflicts of interest with Gladstone Management Corporation and its affiliates, the use of borrowed money to finance our investments, the adequacy of our financing sources and working capital, and our ability to co-invest, among other factors. In some cases, you can identify forward-looking statements by terminology such as “estimate,” “may,” “might,” “believe,” “will,” “provided,” “anticipate,” “future,” “could,” “growth,” “plan,” “project,” “intend,” “expect,” “should,” “would,” “if,” “seek,” “possible,” “potential,” “likely” or the negative or other variations of such terms or comparable terminology. These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from any future results, levels of activity, performance or achievements expressed or implied by such forward-looking statements. Such factors include but are not limited to:

We caution readers not to place undue reliance on any such forward-looking statement, which speak only as of the date made. Actual results could differ materially from those anticipated in our forward-looking statements and future results could differ materially from our historical performance. Except as required by law, we undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, after the date of this prospectus supplement. Although we undertake no obligation to revise or update any forward-looking statements, whether as a result of new information, future events, or otherwise, you are advised to consult any additional disclosures that we may make directly to you or through reports we have filed, or in the future may file with the SEC, including subsequent annual reports on Form 10-K, quarterly reports on Form 10-Q and current reports on Form 8-K. The forward-looking statements contained or incorporated by reference in this prospectus supplement or accompanying prospectus are excluded from the safe harbor protection provided by the Private Securities Litigation Reform Act of 1995 and Section 27A of the Securities Act of 1933, as amended (the “Securities Act”).

TERMS OF THE SERIES [    ] PREFERRED STOCK

P-3

RISK FACTORS

[To be provided.]

USE OF PROCEEDS

[To be provided.]

CAPITALIZATION

[To be provided.]

RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND DIVIDENDS ON MANDATORILY REDEEMABLE PREFERRED STOCK

[To be provided.]

DESCRIPTION OF THE SERIES [    ] PREFERRED STOCK

[To be provided.]

TAXATION

[To be provided.]

UNDERWRITING

[To be provided.]

LEGAL MATTERS

The legality of securities offered hereby will be passed upon for us by Bass, Berry & Sims PLC, Nashville, Tennessee. [Certain legal matters will be passed upon for the underwriters by                    .]

P-4

Gladstone Investment Corporation

            Shares

    % Series [    ] Preferred Stock

(Liquidation Preference $            per share)

PROSPECTUS SUPPLEMENT

                    , 201

P-5