A polymer electrolyte having, in a main chain, a structural unit represented by the following formula (1):

wherein Ar¹ and Ar² independently represent a divalent aromatic groups, m represents an integer of 0 to 3, and X⁺ represents an ion selected from hydrogen ion, an alkali metal ion and ammonium ion, which is excellent in proton conductivity, thermal resistance and strength. The polymer electrolyte is soluble in solvents and has excellent film forming property and recycling efficiency.