A polymer electrolyte membrane comprising a mixed layer that includes an ion migration region and a support having a 3-dimensional network structure, wherein the ion migration region has a structure in which two or more cells including an ion-conducting material border 3 dimensionally, and the polymer electrolyte membrane further comprising a pure layer including only the ion-conducting material on an upper surface, a lower surface, or an upper surface and a lower surface of the mixed layer, wherein a volume ratio of the ion-conducting material included in the mixed layer with respect to a volume of space in the support is greater than or equal to 0.6 and less than or equal to 1 when 1) measuring a mass of the polymer electrolyte membrane and measuring a volume of the pure layer, 2) separating the ion-conducting material from the support by stirring the polymer electrolyte membrane 3 times for 3 hours each at 80°C in a solvent capable of dissolving the ion-conducting material, 3) casting the solution including the ion-conducting material separated from the support on a substrate, removing the solvent by drying the result for 24 hours at 100°C, and then measuring a mass and density of the ion-conducting material, 4) washing the support with methanol, drying the result for 24 hours at 100°C, and then measuring the volume of space in the support, 5) measuring a mass of the pure layer from the density of the ion-conducting material and the volume of the pure layer, and 6) measuring a mass of the ion-conducting material included in the mixed layer through subtracting the mass of the pure layer from the mass of the ion-conducting material, and calculating a volume of the ion-conducting material included in the mixed layer through the mass of the ion-conducting material included in the mixed layer and the density of the ion-conducting material, wherein a thickness ratio of the mixed layer with respect to the total thickness of the polymer electrolyte membrane is greater than or equal to 65% and less than or equal to 95%, wherein a thickness of the mixed layer is greater than or equal to 1 um and less than or equal to 30 μm. 1) measuring a mass of the polymer electrolyte membrane and measuring a volume of the pure layer, 2) separating the ion-conducting material from the support by stirring the polymer electrolyte membrane 3 times for 3 hours each at 80°C in a solvent capable of dissolving the ion-conducting material, 3) casting the solution including the ion-conducting material separated from the support on a substrate, removing the solvent by drying the result for 24 hours at 100°C, and then measuring a mass and density of the ion-conducting material, 4) washing the support with methanol, drying the result for 24 hours at 100°C, and then measuring the volume of space in the support, 5) measuring a mass of the pure layer from the density of the ion-conducting material and the volume of the pure layer, and 6) measuring a mass of the ion-conducting material included in the mixed layer through subtracting the mass of the pure layer from the mass of the ion-conducting material, and calculating a volume of the ion-conducting material included in the mixed layer through the mass of the ion-conducting material included in the mixed layer and the density of the ion-conducting material,