Simultaneous deposition of palladium (Pd) and silver (Ag) on the porous α-alumina tube with desired metal ratio was attempted by electroless plating procedure. Seeding of Pd nano-particles on the alumina surface resulted in effective co-deposition of Pd and Ag. Nano-particles of Pd nuclei were uniformly distributed by dip-coating with palladium acetate or [Pd(acac) 2] (acac: acetylacetonato ion) in organic solvents followed by reduction with alkaline hydrazine solution. Simultaneous deposition of Pd and Ag was achieved from the mixed aqueous solution which consists of ethylendiamine-N,N,N′,N′-tetraacetic acid (EDTA), ammonia, hydrazine and two metal ion species. The Pd/Ag ratio of the membrane film was controlled in the range of 0-30 wt.% by optimizing the chemical composition of plating solution, particularly with respect to the amount of EDTA, ammonia and hydrazine against the given ratio of Pd and Ag. After simultaneous deposition, alloying of Pd and Ag was successfully achieved under mild conditions, i.e. at 500°C for 4 h in hydrogen gas atmosphere due to easy inter-diffusion of two metals. Permeation of H2 and N2 were measured to evaluate perm-selectivity of the alloy membranes. © 2004 Elsevier B.V. All rights reserved.