A partial oxidation of methane was carried our using iridium catalysts supported on several metal oxides. The productivity of the synthesis gas from methane was strongly affected by the choice of support oxides for the catalysts. The synthesis gas production proceeded basically via a two-step reaction consisting of methane combustion to give H2O and CO2, followed by the reforming of methane from CO2 and steam. Although the combustion and the reforming of methane from steam did not depend upon the catalyst support, a large variation in the catalytic activity fbr the reforming of methane from CO2 was observed over Ir catalysts with different supports. The support activity order in the reforming of methane from CO2 with iridium catalysts was as follows : TiO2 greater than or equal to ZrO2 greater than or equal to Y2O3 > La2O3 > MgO greater than or equal to Al2O3 > SiO2. The same order was observed in the synthesis gas production from the partial oxidation of methane.