Palladium composite membranes have the potential for the selective removal and separation of hydrogen and can serve in catalytic membrane reactors at high temperature. However, the success of membranes in these applications will largely depend on the availability of membranes with acceptable permselectivity and thermal stability. In this work, a dense Pd/SS composite membrane with good selectivity for hydrogen and thermal stability was prepared by the electroless plating technique combined with osmosis. The morphology and microstructure of the composite membrane made was characterised by SEM. The newly plated palladium requires an activation process prior to use for separation and catalytic applications. The SEMs demonstrate good adhesion of the plated palladium film on the stainless steel (SS) substrate and dense coalescence of the palladium film. Permeation results showed that the membrane possesses high hydrogen selectivity and thermal stability at high temperature. At 480 degrees C and a differential pressure of 1 bar, the hydrogen permeation flux of the composite membrane is as high as 12 cm(3)/cm(2) min. The hydrogen/nitrogen ratio increased with temperature and was over 1000 at temperatures above 400 degrees C. Separations with mixed gases were also carried out for the composite membrane.