Silica/porous stainless steel (SUS) composite membranes were prepared for carbon monoxide (CO) removal from products of methanol steam reforming. A support was prepared by coating Ni powder with sub-micron level and SiO2 sols with particle size of 500 and 150 nm in turns on SUS. Silica top layer was coated on the modified support using colloidal sol with nanoparticle. As a result of mixture gas permeation test of silica composite membrane using H-2(99%)/CO(1%), CO concentration of 10000 ppm was reduced to under 81 ppm, which is acceptable in polymeric electrolyte membrane fuel cell (PEMFC) anode gas purification. Permeation mechanism through the membrane was mainly molecular sieving. (C) 2003 Published by Elsevier Science B.V.