In the present study, photofermentative hydrogen production on thermophilic dark fermentation effluent (DFE) of sugar beet thick juice was investigated in a solar fed-batch panel photobioreactor (PBR) using Rhodobacter capsulatus YO3 (hup(-)) during summer 2009 in Ankara, Turkey. The DFE was obtained by continuous dark fermentation of sugar beet thick juice by extreme thermophile Caldicellulosiruptor saccharolyticus and it contains acetate (125 mM) and NH4+ (7.7 mM) as the main carbon and nitrogen sources, respectively. The photofermentation process was done in a 4 L plexiglas panel PBR which was daily fed at a rate of 10% of the PBR volume. The DFE was diluted 3 times to adjust the acetate concentration to approximately 40 mM and supplemented with potassium phosphate buffer, Fe and Mo. In order to control the temperature, cooling was provided by recirculating chilled water through a tubing inside the reactor. Hydrogen productivity of 1.12 mmol/L-c/h and molar yield of 77% of theoretical maximum over consumed substrate were attained over 15 days of operation. The results indicated that Rb. capsulatus YO3 could effectively utilize the DFE of sugar beet thick juice for growth and hydrogen production, therefore facilitating the integration of the dark and photo-fermentation processes for sustainable biohydrogen production. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.