In this work, pure CeO2 and three nickel-ceria catalysts prepared by different methods have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in the sulfur-iodine (SI or IS) cycle at various temperatures. BET, XRD, HRTEM and TPR were performed for catalysts characterization. indeed, the pure CeO2 also strongly enhance the decomposition of HI to H-2 by comparison with blank yield. Nickel-ceria catalysts show better catalytic activity, especially Ni-doping-G sample. it is found that, through the sol-gel method, the Ni2+ ions have dissolved into the ceria lattice instead of the Ce4+ ions during the synthesis process of Ni-doping-G sample. Oxygen vacancies are formed because of the charge imbalance and lattice distortion in CeO2. The presence of Ni during the CeO2 synthesis process of Ni-doping-G also causes smaller average particle size, larger surface area, better thermal stability and better Ni dispersion than the Ni-loading samples. These provide nickel-ceria catalyst with a potential to be used in the SI cycle for HI decomposition. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.