Disclosed are a polymer electrolyte membrane, a method of manufacturing the membrane, and a membrane-electrode assembly including the membrane. The polymer electrolyte membrane contains a porous support having a plurality of pores, a first layer including a first ion conductor that fills the pores adjoining one surface of the porous support, and a second layer including a second ion conductor that fills the pores adjoining the other surface of the porous support, wherein the first ion conductor and the second ion conductor are different from each other, and one selected from the group consisting of the first layer, the second layer, and a combination thereof includes an organic-based antioxidant.