Abstract: A solid polymer electrolyte membrane is used to stably generate electricity under non-humidified conditions or conditions with a relative humidity of 50% or less at an operating temperature of 100° C. to 300° C. for a long period of time. A method of producing the same and a fuel cell including the solid polymer electrolyte membrane are also provided. The solid polymer electrolyte membrane comprises a component A comprising at least a basic polymer such as polybenzimidazoles, polybenzoxazoles, and polybenzthiazoles, a component B comprising at least a basic polymer such as a porous polyolefin resin grafted by a vinyl monomer, a porous fluorinated polyolefin resin grafted by a vinyl monomer, and a porous polyimide resin grafted by a vinyl monomer, and a component C comprising at least an inorganic acid such as a sulfuric acid, a phosphoric acid, and a condensed phosphoric acid.