For methane decomposition, Al2O3-supported Ni catalysts were found to be more active and stable than Ni/SiO2 under the conditions employed. The catalyst activities at 823 K were Ni/Ca/Al2O3> Ni/Al2O3> Co/Al2O3> Fe/Al2O3. The carbons formed after 14 h reaction at 823 K were of bent filamentous shape and of graphite-like structure, and metallic Ni particles were located on the tip of the filament, the diameters of which were between 55 and 77 nm.