A novel catalyst, Ni/Ce-ZrO2, exhibits very high catalytic activity and stability even in the stoichiometric steam reforming of methane (H2O/CH4 = 1). Furthermore, when it was employed in oxy-steam reforming, it gave enhanced CH4 conversion (99.1%) at 750 degreesC and the activity was maintained for 100 h. The high catalyst stability is mainly ascribed to the synergistic effect of the Ce modifier resulting from high capacity to store oxygen and high ability to produce mobile oxygen.