Perovskite-type La0.5Sr0.5FeO3-delta and composite Sr0.77Fe0.54Al0.46O2.54-delta exhibit relatively high oxygen permeation fluxes and similar thermal expansion coefficients, (12.4-13.1) x 10(-6) K-1 at 350-950 K and (23.4-23.7) x 10-6 K-1 at 950-1300 K in air. Due to higher sinterability of Sr0.77Fe0.54Al0.46O2.54-delta consisting of strontium-deficient Sr(Fe, Al)O3-delta perovskite and SrAl2O4 phases, such properties enable to combine these materials in asymmetric membranes where dense Sr0.77Fe0.54Al0.46O2.54-delta layer is supported by porous lanthanum-strontium ferrite ceramics. In order to achieve a sufficient porosity and mechanical strength of the supports, various pore-forming agents were tested, including graphite, methylcellulose powder and an aqueous methylcellulose solution. The asymmetric membranes were fabricated adding 2 wt.% graphite into pre-synthesized La0.5Sr0.5FeO3-delta powder, with subsequent co-pressing and co-sintering at 1723 K. As oxygen permeation through Sr0.77Fe0.54Al0.46O2.54-delta ceramics is substantially affected by the oxygen exchange kinetics, the surface of the dense layer can be effectively activated applying a mixture of the composite, metallic Pt and/or praseodymium oxide. At 1023-1173 K the oxygen fluxes through a model asymmetric membrane, with dense layer thickness of 0.5 mm, varied in the range (1-3) x 10(-7) mol s(-1) cm(-2) under the oxygen partial pressure gradient of 21/2.1 kPa. (c) 2005 Elsevier B.V. All rights reserved.