The ethanol steam reforming has been carried out in a membrane reactor consisting of a Ru-based catalyst bed packed into a thin wall Pd-Ag permeator tube produced via cold-rolling and diffusion welding of metal foils. The experimental tests have been performed in the temperature range 400-450 degrees C with the aim of studying the performances of the membrane reactor in terms of hydrogen yields. The main investigated operating parameters have concerned the water/ethanol feed molar ratio (8.4-13.0), the pressure inside the membrane (150-200 kPa), the sweep gas mode (co-current and counter-current) and the spatial velocity. In all the tests, ultra pure hydrogen has been separated through the Pd-Ag membrane: especially, operating at 450 degrees C and 200 kPa, a hydrogen yield higher than 80% has been produced thus demonstrating the membrane ability of promoting the reaction conversion (shift effect). (c) 2007 Elsevier B.V. All rights reserved.