A thin palladium film supported on SiO2-modified porous stainless steel has been fabricated by a novel preparation procedure. SiO2 colloid suspensions with different particle sizes were applied to modify the pore size of the substrate and form an intermediate SiO2 layer to support the palladium layer as well. Palladium nuclei were seeded inside the pores of the modified substrate besides some particles deposited over the surface by a chemical vapor deposition process using Pd(F(6)acac)(2) as the metal precursor, and then a palladium layer of 2-6 mu m was prepared by an electroless plating process. The membrane had a H-2 permeance of 2.7 x 10(-6) mol/m(2.)s(.)Pa and a permselectivity of P-H2/P-N2 in the range of 300-450 measured using single pure gases at a pressure difference of 0.5 x 10(5) Pa and at 773 K. The surface morphology and the components of the different layers of the membrane have been studied by scanning electron microscopy and energy-dispersive X-ray analysis. The permeance and permselectivity of the membranes with different thicknesses have bean measured at different temperatures and pressures. The stability of the membrane during the heat cycles indicated that a stable structure of the composite membrane was fabricated. The transportation mechanism is elucidated based on the analysis.