Fabrication of dense ceramic electrolyte membranes on porous supports is a key step towards performing gas separations (H-2 or O-2) through the electrochemical pathway. This research develops an approach by making use of the electroless plating method for the preparation of metal-ceramic composite membrane, which is used as the precursor to a metal-oxide composite membrane. As a model of the composite membrane, metallic cobalt is incorporated into a powder-packed layer of La0.2Sr0.8CoO3-delta (LSCO-80), which is pre-coated on a porous MgO disk. When this composite membrane is subjected to sintering at 1000degreesC in air, an interpenetrating laminar structure consisting of CoO and LSCO-80 phases is formed according to the cross-section EDX profiles. The oxidation of Co during sintering causes a structure expansion, which exerts a compressive stress on LSCO-80 phase, thus effectively buffering a tensile stress applied by the support. As a result, the composite membrane LSCO-80/CoO can achieve almost gas-tight at ambient temperature.