NOVELTY - A raw material mixture containing silicon alkoxide having methacryloxy alkyl group, at least 1 type of silicon alkoxide, at least 1 type of specific ethylene glycol compound and phosphoric acid compound, is solidified by sol-gel method, to obtain an inorganic-organic composite material. The silicon alkoxide is chosen from trifunctional silicon alkoxide and tetrafunctional silicon alkoxide.    USE - For fuel cell.    ADVANTAGE - The composite material has high proton conductivity even under reduced moisture condition. The composite material has excellent heat resistance, flexibility and chemical resistance.    DETAILED DESCRIPTION - A raw material mixture containing silicon alkoxide having methacryloxy alkyl group, at least 1 type of silicon alkoxide, at least 1 type of ethylene glycol and phosphoric acid compound, is solidified by sol-gel method, to obtain an inorganic-organic composite material. The silicon alkoxide is chosen from trifunctional silicon alkoxide and tetrafunctional silicon alkoxide. The ethylene glycol is polyethylene glycol, polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol monoacrylate and/or polyethylene glycol diacrylate.    An INDEPENDENT CLAIM is included for inorganic-organic composite material consisting of an organic phase and an inorganic matrix phase.    The organic phase consisting of polyethylene glycol, polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol monoacrylate and/or polyethylene glycol diacrylate, is dispersed uniformly in the amorphous inorganic matrix phase containing silica, RSiO3/2 (where R is an alkyl group, phenyl group or methacryloxy alkyl group) and phosphorus pentoxide.    At least 1 type chosen from inorganic matrix, ethylene glycol, polyethylene glycol, polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol monoacrylate, and polyethylene glycol diacrylate, is subjected to hydrogen bonding.