In reforming of CH4 with CO2 over molybdenum carbide catalysts, the catalytic performance of unsupported hexagonal Mo2C prepared by direct carburization of MoO3 was considerably different from a similar composition, cubic MoC1-x (x approximate to 0.5), prepared through nitriding before carburization. The conversion levels over MoC1-x were substantially higher than those over Mo2C, although the turnover frequencies were lower. X-ray diffraction analysis indicated that Mo2C deactivated by conversion to MoO2 during the reaction, but the MoC1-x was transformed to the hexagonal Mo2C and remained stable. The activity of Mo2C dispersed on various supports for the CH4-CO2 reaction was also investigated. The performance depended strongly on the property of supports, with the ZrO2-supported Mo2C catalyst exhibiting the highest activity and durability for this reaction. Moreover, deactivation of Mo2C/ZrO2 at ambient pressure was suppressed by decreasing the loading amount of Mo2C.