A proton-conductive membrane includes a hydrophobic organic polymer and a hydrophilic proton-conductive component. The hydrophilic proton-conductive component includes one of an urea-containing material and a complex formed from an acidic substance and a basic substance, and a combination thereof. The hydrophilic proton-conductive component is present in an amount ranging from 23 parts by weight to 70 parts by weight based on 100 parts by weight of the proton-conductive membrane.