NOVELTY - A gas barrier property solid electrolyte material comprises proton-conductive polymeric material which dissolves in an aprotic polar solvent and has proton-conductive group in chemical structure. The structure (I) contains olefins, and reactive functional group chosen from amino, hydroxyl, halogen, epoxy and isocyanate group, and is bonded with structure (I). The gas barrier property polymeric material is capable of dissolving in the aprotic polar solvent, and the molecular chain has twined round the proton-conductive polymeric material.    USE - Gas barrier property solid electrolyte material is used for membrane electrode assembly (claimed) for fuel cell used as power supply of motor vehicle and domestic electric power generating apparatus.    ADVANTAGE - The gas barrier property solid electrolyte material has excellent gas barrier property and proton conductivity.    DETAILED DESCRIPTION - A gas barrier property solid electrolyte material comprises proton-conductive polymeric material dissolves in an aprotic polar solvent and has proton-conductive group in chemical structure. The structure (I) contains olefins, and reactive functional group chosen from amino, hydroxyl, halogen, epoxy and isocyanate group, and is bonded with structure (I). The gas barrier property polymeric material is capable of dissolving in the aprotic polar solvent, and the molecular chain has twined round the proton-conductive polymeric material. The cross-linked structure cross-links between the reactive functional groups by reacting cross-linking agent with two or more combining functional groups combinable by reacting with the reactive functional group. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of gas barrier property solid electrolyte material, which involves dissolving proton-conductive polymeric material in aprotic polar solvent, and subjecting to dissolution process, and mixing polymeric-material solution, and cross-linking agent with two or more combinable functional groups combinable by reacting with the reactive functional group; and    (2) membrane electrode assembly, which comprises solid electrolyte film having electroconductive electrolyte material which shows a proton and electronic conductivity in portion of thickness direction, and has in remainder the proton-conductive electrolyte material which shows proton-conductivity, fuel electrode provided on one side of solid electrolyte, and the oxidizing agent electrode provided on the other side, and at least one portion of the proton-conductive electrolyte material and/or the electroconductive electrolyte material include the gas barrier property solid electrolyte material.