Photocatalytic H-2 evolution due to the decomposition of water in alkaline solution was investigated using Pt-TiO2 as photocatalyst and iodide ion, KI, as a redox mediator. In order to find the optimum conditions for H-2 evolution, the effect of alkaline concentration, KI concentration, and the amount of Pt loading on the photocatalytic reactivity was examined. The results showed that H-2 evolution depends on the concentration of alkaline solution, KI concentration, and amount of Pt loading. (C) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.