The effect of the oxides of Na, K, Mg, and Ca on CO2-reforming of CH4 over Ni/Al2O3 catalysts was studied from the viewpoint of carbon deposition. These added oxides markedly suppressed the carbon deposition during CO2-reforming, also in the absence of CO2. It was concluded that the suppression of carbon deposition resulted from the decrease in the ability of Ni catalyst for CH4 decomposition. It was also observed that the added basic metal oxides changed the reaction order from negative to positive with respect to the partial pressure of CH4 and from positive to negative with respect to the partial pressure of CO2. The observed reaction kinetics suggested that the surface of the Ni catalyst with basic metal oxides was abundant in adsorbed CO2, while the surface without them was abundant in adsorbed CH4. The abundance in adsorbed CO2 on the Ni metal surface was considered an unfavorable condition for CH4 decomposition and as a result, carbon deposition was further suppressed during CO2-reforming on Ni/Al2O3 catalysts with basic metal oxides.