A commercial hygroscope SiO2 was used as an inorganic filler in a Nafion® polymeric matrix. The influence on chemical-physical properties and electrochemical behaviour in Polymer Electrolyte Fuel Cells (PEFCs) was investigated in terms of amount and particle size of the introduced inorganic compound. Such SiO2 has got a good water retention capacity that improves the water uptake and contributes to improve the stiffness of the developed membranes, probably making more efficacy in the medium temperature operation. Current density values of about 720mW/cm2 and 640W/cm2 at 80{degree sign}C and 110{degree sign}C (0.6V and 100%RH), respectively were reached from the N-SiO2 membrane containing a 5%wt/wt of oxide with a particle size of 7 nm. Such result compared to a home-made bare Nafion membrane showed an important improvement, high lightening the benefit of the inorganic filler when PEFC operates at medium temperature.