Nafion/inorganic (inorganic = S-ZrO2, SiO2-SO 3H, SBA-15-SO3H, MCM-41-SO3H, and P-Si gels) composite membranes were synthesized with the goal of increasing the proton conductivity and water retention at elevated temperatures up to 120 °C and reduced relative humidity (RH) down to 25%. Inorganic materials were incorporated within the Nafion by three different techniques. The addition of inorganic particles increased the membrane ion exchange capacity (IEC). The conductivity of composite membranes with sulfonated inorganic materials was in agreement with their IEC but not higher than the conductivity of the recast Nafion in the whole range of inorganic loading. Conductivity of the Nafion/P-Si gel membranes was affected by the surface of inorganic powders and was higher for membranes prepared by in situ formation techniques. Effect of the inorganic phase on membrane performance in a fuel cell was much stronger than on its conductivity due to substantial improvement in membrane water retention properties.