Filed Pursuant to Rule 424(b)(3)

Registration No. 333-164703

KBS REAL ESTATE INVESTMENT TRUST III, INC.

SUPPLEMENT NO. 5 DATED APRIL 10, 2013

TO THE PROSPECTUS DATED FEBRUARY 6, 2013

This document supplements, and should be read in conjunction with, the prospectus of KBS Real Estate Investment Trust III, Inc. dated February 6, 2013, as supplemented by supplement no. 1 dated February 6, 2013, supplement no. 2 dated February 6, 2013, supplement no. 3 dated March 12, 2013 and supplement no. 4 dated April 2, 2013. As used herein, the terms “we,” “our” and “us” refer to KBS Real Estate Investment Trust III, Inc. and, as required by context, KBS Limited Partnership III, which we refer to as our “Operating Partnership,” and to their subsidiaries. Capitalized terms used in this supplement have the same meanings as set forth in the prospectus. The purpose of this supplement is to disclose the second amended and restated dividend reinvestment plan.

Second Amended and Restated Dividend Reinvestment Plan

On April 9, 2013, our board of directors approved a second amended and restated dividend reinvestment plan (the “Amended Dividend Reinvestment Plan”). Pursuant to the Amended Dividend Reinvestment Plan, in order to terminate participation in the dividend reinvestment plan, a participant must provide us with written notice.  The Amended Dividend Reinvestment Plan reduces the advance notice that a stockholder must provide in order to terminate participation in the dividend reinvestment plan from ten business days prior to the last day of the month to which a distribution relates to four business days prior to the last business day of the month to which a distribution relates.

There were no other changes made in the Amended Dividend Reinvestment Plan. The Amended Dividend Reinvestment Plan will be effective April 20, 2013.

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