In this study, 5%Ni/Ce(1-x)ZrxO2(x = 0, 0.2, 0.5, 0.8, 1) catalysts were prepared by sol-gel method and tested for hydrogen iodide (HI) decomposition in sulfur-iodine (SI) cycle. The effects of zirconia incorporation were subsequently examined by a series of characterization methods. In comparison with the blank test, all of the catalysts, particularly Nil Ce0.8Zr0.2O2, remarkably enhance the HI decomposition. Therefore, adding a small amount of zirconia results in the highest catalytic activity, which could be attributed to the following three effects: increase in oxygen mobility and oxygen vacancy, stronger interaction between NiO and the supports. The oxygen mobility and oxygen vacancy are dominant in the HI decomposition. The strong interaction between NiO and the supports accelerates the oxygen transfer from the bulk to surface, which could also enhance the decomposition. However, excessive zirconia content has negative effects, which is due to the decrease in oxygen mobility and surface area. The poor thermal stability in zirconia-rich supports also restricts catalytic performance. In addition, a hypothetic mechanism of HI catalytic decomposition over Ni/Ce(1-x)ZrxO2 is proposed. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.