This work reports on the preparation and characterization of hybrid membranes based on blends of ethylene-propylene-diene terpolymer (EPDM) and different organophilized silicas. The films obtained were crosslinked to improve mechanical stability, and heterogeneously sulfonated to convert them in proton conducting systems. The structural characterization consisted on the analysis of their thermal and mechanodynamical transitions by DSC and DMA, the verification of the introduction of sulfonic groups by infrared spectroscopy (ATR), and the obtaining of information about the silica location and distribution within the polymer by scanning electronic microscopy (SEM-EDX). The electrical characterization was made using electrochemical impedance spectroscopy (EIS). Also, methanol crossover and water up-take were determined, and the results were compared with those of Nafion (R) 117. Results show that sulfonation of the styrene rings has effectively occurred. Conductivity value is higher and methanol crossover is lower than in Nafion for all experimental samples. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1203-1210,2009