In this study, three Pd and Pd-Ag membranes supported on a porous stainless steel tube were prepared by means of successive sequential electroless plating steps. Pd-Ag alloy membrane was obtained by annealing the resultant Pd and Ag deposited layers at 723K in a hydrogen atmosphere. Hydrogen and nitrogen permeations were conducted at various temperatures and pressures to detect the flow mechanisms that evolved in these membranes and subsequently to differentiate between the dense or porous membranes to which the flow mechanisms belonged. The Pd-Ag membrane showed a hydrogen flux that was over 30 times greater than that of the palladium membrane. Furthermore, the hydrogen fluxes through these dense membranes increased with increasing temperature, while the hydrogen and nitrogen fluxes through the porous membranes decreased with increasing temperature. From the experimental results, it can be concluded that the solution-diffusion mechanism dominated the permeation of hydrogen through the dense membranes, but instead of a combined mechanism of Knudsen diffusion and viscous flow was prevalently conducted in the porous membrane.