The reforming of CH4 With CO2 over supported Rh catalysts has been studied over a range of temperatures (550-1000 K). A significant effect of the support on the catalytic activity was observed, where the order was Rh/Al2O3 > Rh/TiO2 > Rh/SiO2. The catalytic activity of Rh/SiO2 was promoted markedly by physical mixing of Rh/SiO2 with metal oxides such as Al2O3, TiO2, and MgO, indicating a synergetic effect. The role of the metal oxides used as the support and the physical mixture may be ascribed to the promotion in dissociation of CO2 on the surface of Rh, since the CH4 + CO2 reaction is first order in the pressure of CO2, suggesting that CO2 dissociation is the rate-determining step. The possible model of the synergetic effect was proposed.