The present work focuses on the characterization of membranes for direct methanol fuel cells (DMFC), prepared using composites of sulfonated poly(ether ether ketone) (sPEEK, with sulfonation degree, SD, of 42 and 68%) as polymer matrix. This polymer was inorganically modified incorporating different amounts of zirconium phosphate (ZrPh) pretreated with n-propylamine and polybenzimidazole (PBI). The investigated properties were: proton conductivity, water and aqueous methanol swelling, permeability coefficients for DMFC species and morphology. DMFC tests were performed at 110 degrees C with relative humidity (r.h.) in the cathode feed of 100 and 138%. The results obtained show that the inorganic modification of the polymer decreases the proton conductivity, water and aqueous methanol swelling and permeability towards DMFC species. In terms of morphology, it was found that the applied procedure enabled the preparation of membranes with good compatibility between inorganic and organic components. In terms of the DMFC tests of the composite membranes, working with the cathode feed at 100% r.h., the unmodified sPEEK membrane with SD = 42% proved to have the best performance, although with higher methanol crossover. In contrast, for r.h. of 138%, the best performance was achieved by the sPEEK composite membrane with SD = 68 and 20.0 wt.% of ZrPh and 11.2 wt.% of PBI. (c) 2005 Elsevier B.V. All rights reserved.