It has been recently shown than PVDF can be an interesting alternative to Nafion for the fabrication of proton-conducting membranes for polymer fuel cells. To this aim, PVDF (which is hydrophobic in nature) can be structurally modified by radiation grafting with styrene comonomers, which allow to link sulfonic groups. Critical parameters of the process are the energy of the radiation field (electrons, gamma-rays), the absorbed dose, and the physico-chemical properties of the starting polymer (crystallinity degree, porosity, etc.).In this paper we report on the synthesis work and thermal (MDSC), morphological (AFM) and electrical (IS) characterisations of proton-conducting polymers. We compare membranes obtained from the P(VdF-5 mol% HFP) copolymer and from commercial porous and dense PVDF homopolymer films.High grafting degrees and water uptake have been reached depending on the nature of the polymer matrix. Room temperature conductivity exceeding 60 mS/cm at 90% RH has been observed in the case of the sulfonated membrane obtained from the PVDF-based copolymer. In this case, the conduction mechanism and the uptake process have been investigated at different humidity conditions and compared with the data reported for Nation(TM) 117. (C) 2004 Elsevier B.V All rights reserved.