Disclosed are an electrolyte membrane of a membrane-electrode assembly including an electronic insulation layer, which greatly improves the durability of the electrolyte membrane, and a method of preparing the same. The electrolyte membrane includes an ion exchange layer and an electronic insulation layer provided on the ion exchange layer, and the electronic insulation layer includes one or more catalyst complexes, and a second ionomer Particularly, each of the one or more catalyst complex includes a catalyst particle and a first ionomer coated on the entirety or a portion of the surface of the catalyst particle, and the one or more catalyst complexes are dispersed the second ionomer.