Magnetite and inorganic sludge were mainly composed of Fe2O4 and Fe2O3, respectively. Initial specific surface areas of magnetite and inorganic sludge were 130 m2/g and 31.7 m2/g. CO2 decomposition rate for inorganic sludge was increased with temperature. Maximum CO2 decomposition rates were shown 89% for magnetite at 350℃ and 84% for inorganic sludge at 500℃. Specific surface area for magnetite was not varied significantly after CO2 decomposition. However, specific surface area for inorganic sludge was greatly decreased from initial 130 m2/g to approximately 50~60 m2/g after reaction. Therefore, it was estimated that magnetite could be used for CO2decomposition for a long time and inorganic sludge should be wasted after CO2 decomposition reaction.