Composite Nafion-based membranes were prepared and characterized, using hydrated tin oxide as a filler. Water Uptake and proton conductivity were measured as a function of temperature. Methanol crossover through reference Nafion and composite membranes was evaluated by a voltametric method and the electrochemical performance of the membranes was assessed by tests in a single direct methanol fuel cell (DMFC). The formation of the composite improved the properties of Nafion matrix in terms of methanol crossover and DMFC performance, allowing to identify Nafion membrane with 10wt% tin oxide as a suitable electrolyte to be used in a DMFC device operating at T 90°C.