Commercially available asymmetric porous stainless steel (APSS) tube filters with a smooth top layer were employed as substrates for preparing thin Pd-based composite membranes. The simple electroless plating and electroplating methods cannot successfully prepare defect-free thin (less than 6 mu m) Pd-based membranes on the APSS substrates. Using the improved electroless plating technique based on a multidimensional plating mechanism, it is easy to prepare thin defect-free (less than 6 mu m) Pd/APSS composite membranes. The heat treatment of the APSS substrates has an important effect on membrane performance. The as-prepared 3-mu m Pd/APSS composite membrane under optimum conditions has a hydrogen flux as high as 0.409 mol/(m(2) s) at 773 K with a pressure difference of 100 kPa while keeping the complete hydrogen selectivity versus helium. The stability of the hydrogen flux and the hydrogen selectivity were also proven by operating times as long as 200 h and gas-exchanging cycles as many as 40.