In this work, three catalysts, Ce0.99Pt0.01O2 called the Pt-doping sample, Pt/CeO2 called the Pt-loading sample and pure CeO2, have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in sulfur-iodine (SI or IS) cycle at various temperatures. BET, XRD, TPR and TEM were performed for catalysts characterization. Platinum was introduced into ceria to form the Pt-doping sample by sol-gel. It was found that, through sol-gel method, the Pt ions could be inserted into the ceria lattice. This brought about a different synergistic effect between the Pt and Ce components in the Pt-doping sample by comparison with the Pt-loading sample prepared by traditional impregnation, such as increase of the oxygen mobility in ceria support and improvement of the thermal stability of catalyst. Indeed, the pure CeO2 also strongly enhances the decomposition of HI to H-2 by comparison with blank yield, and the Pt-doping and Pt-loading samples show better catalytic activity, especially the Pt-doping sample. These provide this material with a potential to be used in SI cycle for hydrogen iodide decomposition. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.