The catalytic performance of metal sulfides of Mo and W was studied for the CO2-reforming of methane by comparing with that of Ni/SiO2. The sulfide catalysts have lower activity than the Ni/SiO2 catalyst for this reaction, however, no deactivation due to carbon deposition was observed on the sulfide catalysts. The activity for direct decomposition of CH4 was much smaller on the sulfides than on supported Ni. The rate equation suggested that, during steady-state reaction, the surface was abundant in adsorbed CO2 on sulfides, by which direct decomposition of CH4 should be retarded in addition to their lower activity for this reaction.