Proton-conducting organic-inorganic hybrid membranes containing sulfonic acid groups as proton donor were prepared from porous glasses and an organosilane. We found that silanol groups on pore surfaces react one-to-one with organosilane molecules and that the pore surface was covered by sulfonic acid groups. Proton conductivity of the hybrid membranes was 1.25 x 10(-1) S cm(-1) at 140 degrees C under 100% relative humidity. The conductivity was dependent upon the pore size because of the capillary condensation of water and the friction of water molecules. The membranes were thermally stable up to 140 degrees C. They were chemically stable in methanol because the framework structure of these membranes consisted of porous inorganic glass. (c) 2005 Elsevier B.V. All rights reserved.