Dispersion of submicronic particles of phosphatoantimonic acid fillers (H3) with a 4.3 H+/kg (4.3 eq/kg) cationic exchange capacity (cec), in a solution of sulfonated polysulfone (PSS) of 1.07 H+/kg gives viscous suspension allowing the ＇filled＇ material to be shaped in thin films. From the conductivity measurements, a synergic effect between the acidity of PSS and H3 has been highlighted. Conductivity values close to those of the Nafion 117 have been determined in the same experimental conditions, i.e., 96% relative humidity at 80 degrees C, Furthermore, the inorganic Filler improves both the mechanical strength and the gas impermeability of the filled membrane as compared to an unfilled PSS membrane. A PSS-H3 membrane of 1.07 H+/kg cec filled with 7.1% in H3 provided 80% of Nafion performances in a H-2/O-2 fuel cell for 500 h at 80 degrees C and 4 bars pressure of H-2 and O-2.