The electrochemical characterization of proton-conducting membranes prepared by irradiation-induced grafting and subsequent sulfonation of PVDF films has been performed. In particular, measurements of the ionic conductivity, oxygen solubility and diffusion in the membranes are presented, as well as kinetic data for the oxygen reduction reaction in a membrane-platinum system and a simulation of the performance of these PVDF-g-PSSA membranes in a solid polymer electrolyte fuel cell using a micro-cathode technique. At sufficient degrees of grafting (> 40%) the conductivity reaches 0.1 Scm(-1), well above that of Nafron 117 (DuPont). The PVDF-g-PSSA membranes show lower solubilities and higher diffusion coefficients of oxygen and a higher water uptake than Nafion 117. The microcathode measurements indicate that those PVDF-g-PSSA membranes which have a conductivity higher than that of Nafion 117 may also give improved performance in fuel cell conditions provided that they have the necessary mechanical and chemical stability.