The surface properties of carbided molybdena-alumina were investigated through O-2-TPD and TPSR along with the catalytic activities of the supported catalysts for CO2 hydrogenation. The 1173 K-carbided catalyst exhibited the highest activity for the reaction on the CO adsorption basis. H-2 pretreatment of the passivated 973 K-carbided catalyst at 773 K did not affect the activity for CO2 hydrogenation but a change was visible for the unpassivated catalyst. Through O-2-TPD, it was found that the adsorbed oxygen oxidizes the surface carbon of the molybdenum carbide to form CO2 and CO. A possible reaction scheme for the hydrogenation of CO2 is given, along with an explanation for the lowered activity of the passivated catalysts. eta-Mo3C2 serves as an active site for CO2 hydrogenation. TPSR results were correlated with the activity to reveal that the number of Mo carbides depends on the activity for CO2 hydrogenation.