Composite asymmetric Pd-Au membranes were prepared on porous Inconel and Hastelloy tubular supports by electroless deposition and galvanic displacement techniques and tested both before and after Au deposition in pure H-2 atmosphere. The final membranes with average Au bulk content up to 16.7 wt % were 9-15 mu m thick and showed H-2/He ideal selectivities in excess of 900 for the entire period of their characterization. The annealing of the as-prepared membranes was conducted through the coating and diffusion mechanism in He and H-2 atmospheres at 500 degrees C. The annealing conditions were chosen after nonisothermal and isothermal HT-XRD studies were carried out on Pd-Au coupons prepared with the same techniques used for the membranes fabrication. After the formation of the Pd-Au layer, the membranes showed steady H-2 flux and stable Au gradient on the membrane top layer. Comparisons between permeance for Pd-Au and pure Pd membranes indicated that the membranes with an average Au bulk content of 4.5 and 5.4 wt % had an enhancement up to 20% of the H-2 permeability with respect to pure Pd membranes in the temperature range 250-450 degrees C. On the other hand, the membrane having the highest Au concentration, even though characterized by a lower H-2 permeability (77% of pure Pd), had a rather high surface Au content (approximately 46 wt %), which might improve the tolerance against H2S poisoning.