We previously found catalytic activity for methane steam reforming in atomized Ni3Al powder which was pretreated by acid and subsequent alkali leaching. In this study the catalytic stability of the pretreated Ni3Al powder was investigated by isothermal test in the temperature range of 873-1173 K for 10 h. The activity was relatively stable over time at low temperatures below 973 K, especially at 873 K, where it retained the initial activity even after 10 h. However, it rapidly decreased with time at temperatures above 1073 K. Fine Ni particles, which were produced on the outer surface of Ni3Al powder during the pretreatment and served as a catalyst, survived on the surface after tests at all the temperatures. They remained almost unchanged below 973 K, leading to the good stability, while sintering and oxidation occurred at high temperatures, leading to the rapid deactivation. (C) 2007 Elsevier B.V. All rights reserved.