An electrolyte membrane of a membrane-electrode assembly has improved chemical durability. The electrolyte membrane includes a composite, which includes an antioxidant in an ionic state and a first ionomer surrounding the antioxidant. The composite is dispersed in a second ionomer, which is a polymer matrix. A manufacturing method for the electrolyte membrane includes preparing an antioxidant solution, mixing the antioxidant solution and a first ionomer dispersion solution, drying the mixture to produce a composite having an antioxidant and a first ionomer surrounding the antioxidant, introducing and mixing the composite with a second ionomer dispersion solution, and applying that mixture to a substrate and drying the mixture to manufacture an electrolyte membrane.