A membrane-electrode assembly for a solid polymer fuel cell, which comprises a mutually opposing anode catalyst layer and cathode catalyst layer with a polymer electrolyte membrane formed between the anode catalyst layer and cathode catalyst layer, wherein the anode catalyst layer and cathode catalyst layer each contain a catalyst and a hydrocarbon-based polymer electrolyte with an ion-exchange group. If the ion-exchange group density of the anode catalyst layer is represented as α [μeq/cm2] and the ion-exchange group density of the cathode catalyst layer is represented as β [μeq/cm2], then α and β satisfy the following relational expressions (1), (2) and (3). β/α>1.0  (1) α