Reaction characteristics of CO2 separation have been investigated in a thermogravimetric analyzer and packed bed reactor using CaO for the removal of CO2 in a syngas produced from the gasification of combustible wastes. Reactions of CaO with CO2 were fitted well by the rate equation of shrinking core model at the product layer diffusion control regime. Furthermore, the reaction order and the activation energy were found as 1.95 and 104 kJ/mol, respectively. Reaction rates of CaO does not increases with the increase of operating pressures, which might be because CaO has macropores in the particle inside and reaction is carried out by the surface solid diffusion. The presence of H2 and CO inhibits the CO2 removal reaction by the water gas shift reaction and reduction of CaO above the temperature of 700 ℃. On the other hand, the CO2 removal reaction was not affected below 600 ℃.