Perovskite La0.2Sr0.8CoO3-delta (LSCO-80) was selected as a model mixed-conductive material for the fabrication of a ceramic electrolyte membrane on porous MgO and ZrO2, disks. Aiming at overcoming mechanical cracks in the membrane caused by thermal mismatch between the membrane and the asymmetric support, Pd/Ag alloy phase was introduced into the LSCO-80 membrane through a non-powder-blending technique. The alloy phase not only offers relevant plasticity to buffer thermal stress generated in the membrane but also possess adequate chemical stability at high temperature. The metallization was carried out on the LSCO-80 membrane by silver slurry coating and followed by electroless palladium plating. Subsequently, the overlaying metal bi-layer was annealed to allow the formation of Pd/Ag-LSCO-80 composite. The metallization could satisfactorily cure mechanical cracks arisen from sintering of the LSCO-80 powder-packing layer. To pursue further promotion of mechanical stability of the composite membrane at high temperature, the LSCO-80 powder was modified by covering individual particles with a Pd/Ag thin layer, which has been proven to be an effective complement to the above coating approach. In addition to focusing on the alloy-assisted mechanical enhancement, this work has also investigated ionic conduction behavior of three different composite membranes by measuring their AC impedances. The results suggest that the metallization improves anionic oxygen conductivity in the perovskite LSCO-80 lattice at high temperatures. This phenomenon is ascribed to a fast cathodic process wherein the Pd/Ag phase plays the key role. (C) 2003 Elsevier B.V. All rights reserved.