Composite membranes based on sulfonated polyether ether ketone (SPEEK) and hydrated tin oxide (SnO2 center dot nH(2)O) were prepared and characterized. The formation of the composite substantially modified the properties of SPEEK in terms of durability and electrochemical performance. The structural and electrochemical performance of the samples were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, electrochemical impedance spectroscopy (EIS), water and methanol uptake (WU, MU), and direct methanol fuel cell (DMFC) tests. The polymer electrolyte membrane doped with 50 wt% SnO2 center dot n(H2O) possess good proton transport characteristics, reduced methanol uptake and improved stability with respect to a reference unfilled membrane and it is then suitable for application as electrolyte in DMFCs. (C) 2007 Elsevier B.V. All rights reserved.