Pd-Ag/porous stainless steel asymmetric membranes were prepared by successive palladium and silver platings in electroless hydrazine baths, followed by a thermal treatment in hydrogen of the as-deposited membranes above the Tamman temperatures for the alloy formation. The prepared membranes were permselective toward hydrogen separation. A membrane reactor made of stainless steel was designed to perform methane steam reforming. At mild reaction conditions, methane conversion is significantly enhanced by partial removal of nydrogen from the reaction location as a result of diffusion through the Pd-based membrane. These effects were examined under a variety of experimental conditions.