NiO/Ce-ZrO2/theta-Al2O3 catalysts were prepared and investigated after the reduction treatment in methane-reforming reactions such as steam reforming and oxy-steam reforming. Among the catalysts with various Ni loading values, 12% Ni loading exhibited not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between Ni and support results in forming stable NiOx species. It is speculated that the populations of NiOx compared with NiO and/or NiAl2O4 play very important roles in the catalytic activity and stability. Metallic Ni sites reduced from NiOx, species strongly interacting with the support are active sites for methane-reforming reactions and have high coke resistance. The high activity and stability of Ni/Ce-ZrO2/theta-Al2O3 is due to a Ce-ZrO2 layer precoated on theta-Al2O3, which plays a role in forming stable NiOx species rather than free NiO or inactive NiAl2O4 and in giving mobile oxygen species. (C) 2003 Elsevier B.V. All rights reserved.