Asymmetric membranes consisting of palladium, ruthenium and platinum deposited on the surface or inside the pores (average size, 200 nm) of a tubular alumina membrane were prepared by the chemical vapor deposition (CVD) technique. Sublimation and decomposition temperatures of their acetylacetonato complexes used as metal sources for CVD were important factors in preparing the membranes selected for hydrogen separation. Among the membranes prepared by CVD, the palladium membrane gave the highest flux of hydrogen and was about 1.6 times higher than a dense palladium membrane with a thickness of 4.5 mu m prepared by an electroless plating technique. The hydrogen permeation through the membranes prepared by CVD are related to the surface diffusion of spillover hydrogen.