Absorption/desorption property of In-doped BaFeO_3-δ, which are candidates for CO₂ absorbents and oxygen storage materials, was evaluated using thermogravimetry-differential thermal analysis (TG-DTA). X-ray diffraction measurements revealed that the crystal structure changed by 10% In substitution from BaFeO_3-δ with ordered distribution of oxide ion vacancy to cubic perovskite structure with random arrangement of oxide ion vacancy and increase in the average valence of Fe ions. From TG-DTA under CO₂ flow, it was found that the CO₂ absorption property could be controlled by the substitution, indicating that CO₂ absorption property would be tunable to required operating condition. Oxygen desorption behaviour of perovskite BaFe_1-xIn_xO_3-δ was evaluated using TG-DTA under various oxygen partial pressures and iodometry. It was found that the amount of oxygen desorption improved by the substitution, which could be attributed to the random distribution of oxide ion vacancy in the lattice.