A polymer electrolyte membrane including an ionic conducting polymer and a light-irradiated product of a photoacid generator (PAG), a method of manufacturing the same, and a fuel cell using the same. The polymer electrolyte membrane has excellent proton conductivity and homogeneity by radiating light such as UV light onto the PAG, thereby producing an acid radical which generates an acid. The polymer electrolyte membrane also suppresses methanol crossover well. The polymer electrolyte membrane can be used as an electrolyte membrane of a fuel cell, for example, a direct methanol fuel cell.