NOVELTY - An electrolyte material is made of a copolymer comprising repeating units based on fluorine-containing monomer and repeating units based on tetrafluoroethylene. The electrolyte material has an ion exchange capacity of 0.9-1.5 meq/g dry resin.    USE - For polymer electrolyte fuel cell.    ADVANTAGE - The inventive electrolyte material has ion conductivity and durability equal to conventional electrolyte material and can be produced at low cost in a shorter process. It has higher softening temperature than the polymer electrolyte material widely used in applications to fuel cells and is more suitable for operation at high temperature than the conventional material.    DETAILED DESCRIPTION - An electrolyte material is made of a copolymer comprising repeating units based on monomer of formula CF2=CFCF2OCF2CF2SO3H (I) and repeating units based on tetrafluoroethylene. The electrolyte material has an ion exchange capacity of 0.9-1.5 meq/g dry resin.    INDEPENDENT CLAIMS are also included for:    (A) production of electrolyte material by subjecting tetrafluoroethylene and monomer of formula CF2=CFCF2OCF2CF2SO2F (II) to radical copolymerization in the presence of perfluoro compound initiator at 60-100degreesC, or subjecting tetrafluoroethylene and monomer (II) to radical copolymerization in the presence of hydrocarbon type initiator at greater than or equal to20degreesC - less than 50degreesC;    (B) a copolymer comprising repeating units based on monomer (II) and repeating units based on tetrafluoroethylene, and having Tq of 200-400degreesC as an index of the molecular weight and an ion exchange capacity of 0.9-1.5 meq/g dry resin, when converted to -SO3H form; and    (C) a polymer electrolyte fuel cell including an anode, a cathode, and a polymer electrolyte membrane made of the above electrolyte material, disposed between the anode and cathode, and having a thickness of 5-70 microns; or an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and cathode, where at least one of the anode and cathode has a catalyst layer comprising a catalyst and a copolymer comprising repeating units based on monomer (I) and repeating units based on tetrafluoroethylene.