An object of the present invention is to provide a membrane-electrode assembly for solid polymer electrolyte fuel cells, which can impart high electrical properties by increasing the introduction amount of the sulfonic acid group, has excellent swell suppression effect even under the humidified condition of high-temperature, and which has excellent electrical properties even under the condition of high-temperature and low-humidity. By using sulfonated polyarylene having specific constitutional units as a proton conductive membrane, a membrane-electrode assembly for solid polymer electrolyte fuel cells can be provided which has excellent swell suppression effect even under the humidified condition of high-temperature, and which has excellent proton conductivity even under the condition of high-temperature and low-humidity.