Defect free palladium (Pd) and gold (Au) alloy membranes (4-5μm thickness) supported on the porous α-alumina tubes were fabricated by electroless plating technique followed by thermal annealing. Contents of Au were adjusted from 0 to 10 mass% by controlling the concentration of K[Au(CN) 4] in the electroless plating solution. The alloy membranes were characterized by the X-ray diffraction analysis, SEM observation, and elemental analysis with EDX and ICP-atomic emission spectrophotometry (ICP-AES). The performances of the Pd-Au alloy membranes were evaluated with respect to the hydrogen flux, perm-selectivity and long term operation tested at 600°C. © 2008 The Japan Institute of Metals.