The mechanism Of CO2 gasification of carbon catalyzed with alkaline earth catalyst (Ca, Sr, Ba) was investigated with pulsed reaction and temperature programmed desorption techniques using labeled CO2. Several reaction paths similar to those of alkali metals were observed in both the oxidation of the catalyst and the reduction of the catalyst. Dispersed alkaline earth metal oxide and metal oxide cluster or alkaline earth metal cluster containing a large amount of oxygen were the main surface species. The catalysts oxidation by CO2 and reduction with carbon proceed on these sites but characteristic features of these sites were quite different between Ca and Ba or Sr. The reaction patterns of Ba- and Sr-loaded carbon were very similar to those of Li-loaded one. A weak interaction between the metals and carbon and strong interaction between the metals and oxygen in the cluster are suggested for Ba and Sr. The reaction patterns of Ca were quite different from those of Ba and Sr and strong interaction between the cluster and carbon is suggested.