Sr1+xCo0.8Fe0.2O3 (0.2 <= x <= 0.1) oxides have been synthesized and investigated as potential oxygen absorbents for high temperature oxygen separation processes. It was found that the A-site ion deficient Sr0.95Co0.8Fe0.2O3 and Sr0.9Co0.8Fe0.2O3 oxides have larger oxygen absorption capacities, and slightly higher oxygen desorption rates. However, the A-site ion excess Sr1.05Co0.8Fe0.2O3 and Sr1.1Co0.8Fe0.2O3 exhibited much higher oxygen desorption rates, but smaller oxygen absorption capacities. The oxygen absorption capacities were further verified using oxygen temperature-programmed desorption technique, and the oxygen desorption rates were well described by a pseudo-second-order kinetics model. In addition, the long-term stability of Sr0.9Co0.8Fe0.2O3 was investigated for 280 h (1120 loops) with switching between oxygen absorption and desorption. The excellent stability was confirmed by X-ray diffraction patterns which suggested that the cyclic processes of oxygen absorption and desorption took place between the perovskite structure with disordered oxygen vacancies and the brownmillerite structure with ordered oxygen vacancies. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 87-95, 2011