A sulfonated poly(arylene ether) copolymer that has a crosslinking structure in a chain of a polymer, a sulfonated poly(arylene ether) copolymer that has a crosslinking structure in and at an end of a chain of a polymer, and a polymer electrolyte film that is formed by using them are disclosed. According to the polycondensation reaction of the sulfonated dihydroxy monomer (HO—SAr1-OH), the none sulfonated dihydroxy monomer (HO—Ar—OH), the crosslinkable dihalide monomer (X—CM-X) and the none sulfonated dihalide monomer (X—Ar—X), the poly(arylene ether) copolymer in which the sulfonic acid is included is synthesized. The formed poly(arylene ether) copolymer has the crosslinkable structure in the chain of the polymer. In addition, by carrying out the polycondensation reaction in respects to the crosslinkable monohydroxy monomer or the crosslinkable monohalide monomer, the crosslinking can be formed at the end of the polymer. Through this, the thermal stability, the mechanical stability, the chemical stability, the film formation ability and the like is the same as or better than those of the Nafion film that is currently commercialized and is used as the polymer electrolyte film, and the proton conductivity and the cell performance are excessively improved. In addition, even though it is exposed to the moisture over a long period of time, since there is no change in the property of the electrolyte film, the dimensional stability is high.