An asymmetric-structured membrane, in which a dense thin La0.6Ca0.4CoO3 layer of 10 mu m was deposited on porous La0.6Ca0.4CoO3 support by a slurry dropping method, were tested for its oxygen permeability at 630-930 degrees C. In order to increase the oxygen permeability, porous La0.6Ca0.4CoO3 and SrCo0.8Fe0.2O3-delta oxygen evolution layers were attached on the dense layer. It was found that the asymmetric structured membranes with the porous oxygen evolution layers showed remarkably higher oxygen permeability as compared with a conventional sintered disk-type membrane (1200 mu m). This suggests that oxygen permeation through membranes of 10 mu m in thickness is rate-determined by both bulk O2- diffusion and oxygen evolution reaction. The maximum oxygen permeability reached 4.77 cm(3) (STP) min(-1) cm(-2) (3.54 x 10(-6) Mol cm(-2) s(-1)) at 930 degrees C for the asymmetric membrane with porous La0.6Ca0.4CoO3 oxygen evolution layer of 10 mu m in thickness (STP= Standard Temperature and Pressure). Further improvements in the oxygen permeability would be achieved through control of the micro-structure of the oxygen evolution layers. (C) 2008 Elsevier B.V. All rights reserved.