Thin (less than 2 mu m thickness) and dense palladium/nickel (Pd/Ni) alloy composite membrane has been fabricated on mesoporous stainless steel (SUS) support modified with submicron nickel powder and CuCN solution. The deposition layer was made by the vacuum electrodeposition technique employing Pd/Ni complex reagent. The deposition layer depended on the experimental condition, especially the current density having an important effect on thickness, composition, and microstructure of deposited Blm. The composition and phase structures of the alloy film were studied by energy dispersive electroscopic analysis (EDS) and X-ray diffraction (XRD); Alloy films prepared with lower current density resulted in smaller grain size and higher Pd content. Also, composite membranes prepared at lower current density showed higher hydrogen permeance and greater hydrogen/nitrogen selectivities. For the current density of 6.5 mA/cm(2), the hydrogen permeance was 2.0 x 10(-2) cm(3)/cm(2) cm Hg s and hydrogen/nitrogen (H-2/N-2) selectivity was 3000 at 723 K.