A process of simultaneous hydrogen production and H2S removal has been investigated over a highly active composite photocatalyst made of bulk CdS decorated with nanoparticles of TiO2, i.e. CdS(bulk)/TiO2. The photocatalytic activity was evaluated for hydrogen production from aqueous electrolyte solution containing H2S dissolved in water or alkaline solution under visible light irradiation. The rate of hydrogen production from the H2S-containing alkaline solution was similar to the rate obtained from photocatalytic hydrogen production from water containing sacrificial reagents (Na2S + Na2SO3) in the similar concentration. The isotope experiment was carried out with D2O instead of H2O to investigate the source of hydrogen from photocatalytic decomposition of H2S dissolved in H2O or alkali solution under visible light. Hydrogen originated from both H2S and H2O when the reaction solution contained H2S absorbed in alkaline water. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.