Ba0.8Sr0.2Co0.8Fe0.2O3-delta (BSCF) membranes were prepared at different sintering conditions. X-ray diffraction (XRD) patterns revealed that the BSCF oxides had a perovskite-related structure with mixed-phase. Slight difference in crystal structures was found for membranes prepared at different sintering conditions including sintering temperature and dwell time. Compared with dwell time, sintering temperature was found to have more influence on the microstructure of membrane. Oxygen permeation flux did not increase directly with the relative density, which was considered to be the combinative result of the microstructure and the crystal structure. (C) 2003 Published by Elsevier Science B.V.