Pd and Pd-Ag alloy membranes on porous alumina tubes were prepared by means of simultaneous and sequential electroless plating technique. The characterizations of Pd-Ag composite membranes were performed using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic reaction of H-2 and O-2 to directly form hydrogen peroxide was carried out in the membrane reactor at 293 K. The thickness of Pd-Ag alloy membranes obtained by simultaneous electroless plating was thinner than that by sequential electroless plating. And high uniformity of grains was found on the surface of the Pd-Ag membrane prepared by simultaneous electroless plating. The concentration of H2O2 increased with the increase in transmembrane pressure differences of hydrogen and a high concentration of H2O2 was obtained on the membrane which consists of a Pd layer on the surface of the membrane and a Pd-Ag alloy layer inside the membrane. (c) 2007 Elsevier B.V. All rights reserved.