In this investigation, we studied the oxidative steam reforming reaction of ethanol in a Pd-Ag/PSS membrane reactor for the production of high purity hydrogen. Palladium and silver were deposited on porous stainless steel (PSS) tube via the sequential electroless plating procedure with an overall film thickness of 20 mu m and Pd/Ag weight ratio 78/22. An ethanol-water mixture (nwater/nethanol = 1 or 3) and oxygen (noxygen/nethanol = 0.2. 0.7 or 1.0) were fed concurrently into the membrane reactor packed with Zn-Cu commerical catalyst (MDC-3). The rection temperatures were set at 593-723 K and the pressures at 3-10 atm. The hydrogen flux in the permeation side icnreased proportionately with increasing pressure; however it reduced slightly when increasing oxygen input. This is probably due to the fast oxidation reaction that consumes hydrogen before the onset of the steam reforming reaction. The effect of oxygen plays a vital role on the ethanol oxidation steam reforming reaction, especially for a Pd-Ag membrane reactor in which a higher flux of hydrogen is required. The selectivity of CO2 increased with increasing flow rate of oxygen, while the selectivity of CO remained almost the same. (c) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.