The reaction kinetics of the CO2 absorption by Ba2Fe2O5, which shows a reversible reaction with CO2 represented as Ba2Fe2O5 + CO2 reversible arrow BaCO3 + BaFe2O4, was investigated by thermogravimetry under various CO2 partial pressures [P(CO2)s]. The calculated Ellingham diagram of the reaction was found to show agreement with the variation in the equilibrium temperature of the reaction with P(CO2). The results of the morphology observation, specific surface area analysis, and TG measurement suggested that the CO2 absorption mechanism of Ba2Fe2O5 is described by a superficial reaction, a diffusion-controlled process, and a sintering reaction as the reaction proceeds. The kinetics of CO2 absorption for the diffusion-controlled process has been analyzed with the Jander function, showing that the activation enthalpy was about 1.6 x 10(2) kJ/mol.