Composite Nafion-based membranes were prepared and characterized, using an organosilane derivative (sulfonated diphenylsilanediol, SDPSD) as a filler. The formation of the composite substantially modified the properties of the Nafion matrix in terms of proton conductivity and thermal stability. The structural and electrochemical performance of the membranes were investigated by means of electrochemical impedance spectroscopy, differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM) and water uptake measurements. Both conductivity values and thermal features of the composite Nafion/SDPSD demonstrated that it has satisfactory proton conductivity values up to 160°C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature. copyright The Electrochemical Society.