TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Film: The proton-conductive polymer is obtained by copolymerizing a compound having one or more sulfonic acid group and one or more ethylenically unsaturated bond in a molecule, a reactive emulsifier and a compound (A) of formula (R1O)n-Si-R2m.R1=4C or less alkyl group;R2=arbitrary organic groups, preferably epoxy, styryl, methacryloxy, acryloxy and/or vinyl group;n, m=1-3;andm+n=4when m is 2 or 3, R2 is a different organic group. The film is obtained by laminating a dispersion liquid containing inorganic particle and organic particle, on an inorganic porous membrane, followed by baking. The primary average particle diameter of inorganic particle is 10-100 nm. The proton-conductive polymer has a crosslinked structure. The reactive emulsifier has a sulfonic acid group. The average pore diameter of the porous membrane is 10-450 nm. The porosity of inorganic porous membrane is 40-95%. Preferred Method: After laminating a dispersion liquid containing 5-60 volume% of inorganic particle and 40-95 volume% of organic particle, on an inorganic porous membrane, a compound having one or more sulfonic acid group and one or more ethylenically unsaturated bond in a molecule, compound (A) and a reactive emulsifier are filled in the pores of the porous membrane. Baking is performed followed by polymerization. Lamination of the dispersion liquid is performed, by an application process. EXAMPLE - A mixture containing 70 volume% of polystyrene microparticles 5008B of average particle diameter 80 nm and 30 volume% of colloidal silica Snowtex 50 of average particle diameter 20 nm, was stirred and dispersed. The obtained dispersion liquid was applied on a polyethylene terephthalate support and dried. Heating was performed followed by baking at 1000degreesC for 3 hours, to obtain a porous membrane. Isopropyl alcohol and water were mixed at mass ratio of 4:1. (2,2'- azobisisobutyronitrile), N,N-methylene bis acrylamide, 2-acrylamide-2-methyl propane sulfonic acid, 3-glycidoxy propyl trimethoxy silane and Aqualon KH-05 were added at a mass ratio of 100:15:5:5:1. The porous membrane was immersed into the obtained liquid mixture under reduced pressure. Heating was performed at 60degreesC for 2 hours. Temperature was maintained at 80degreesC or more for 2 hours, to obtain a proton-conductive electrolyte film of average film thickness 150 microns. The obtained proton-conductive electrolyte film had proton conductivity of 6.3x10-2 S/cm2 and methanol permeability of 0.79 micronsol/(minute.cm2).