Effects of microstructure of carbon supports for platinum catalyst and of perfluorosulfonate-ionomer (PFSI) distribution in the microstructure of the catalyst layer on the consequent performance of polymer-electrolyte fuel cells, prepared by a new method based on the process of PFSI colloid formation, were investigated by electrochemical techniques, a mercury pore sizer, N-2 adsorption [Brunauer-Emmett-Teller and Barrett-Joyner-Halenda] methods, and CO adsorption. The microstructure of the catalyst layer and its effect on polymer-electrolyte fuel cell performance were affected by the contents of PFSI and carbon supports. The PFSI were distributed in the distinctive pores of 0.04 to 1.00 mu m. Pore volume and pore diameter were primarily affected by the carbon supports. Carbon supports had a large pore volume with pore diameters less than 8 nm on the surface of the primary particles. Polymer-electrolyte fuel cell performance predominantly increased with the specific volume of pores covered with the PFSI in the catalyst layer and with a decrease of the specific volume of pores less than 8 nm without PFSI on the carbon surface.