Thin dense films of Ca0.8Sr0.2Ti0.7Fe0.3O3-alpha (CSTF) perovskite-type oxide, which is used as an oxide ionic and electronic mixed conductor, were prepared on a CSTF porous substrate using spin coating method. For use as both thin dense film materials and porous substrates, these CSTF materials were prepared using different procedures. A porous substrate was prepared by treating carbon and CSTF composites in air at 1273 K to produce open pores by carbon combustion. The dense film thickness was controlled at 35-96 mu m by varying the spin coating times. The maximum oxygen flux from air to nitrogen through the asymmetric membrane observed at 1223 K was 2.1 ml min(-1) cm(-2) for 35 mu m film thickness. Oxygen permeation rates were inversely related to the film thickness. These results suggest that bulk diffusion controls the permeation of oxide ion in the CSTF thin film. (C) 2007 Elsevier B.V. All rights reserved.