The oxygen nonstoichiometry of La0.6Sr0.4Co1-yFeyO3-delta (y = 0.2, 0.4, 0.6, 0.8) was measured by high temperature gravimetry and coulometric titration. The results of the oxygen nonstoichiometry measurements could be categorized into Co rich compounds (y = 0.2, 0.4) and Fe rich compounds (y = 0.6, 0.8). The Co rich compounds decomposed into A(2)BO(4) and CoO at relatively high P-O2, i.e. ca.10(-9) bar at 873 K, and ca. 10(-6) bar at 1073 K. The apparent decomposition P-O2 in the case of the Fe rich compounds shifted to the lower P-O2 side, i.e. ca.10(-21) bar at 873 K, and ca. 10(-15) bar at 1073 K. Before reaching this P-O2, the gradual decomposition of the Fe rich compounds was observed by atmosphere controlled high temperature XRD. From the results of the measurement procedure dependence of the coulometric titration data, the actual decomposition P-O2 of the Fe rich compounds can be considered almost comparable to those of the Co rich compounds. (C) 2010 Elsevier B.V. All rights reserved.