Nafion/poly(vinylphosphonic acid) blends were synthesized and characterized in this work. Poly(vinylphosphonic acid), PVPA, was synthesized by the free-radical polymerization of vinylphosphonic acid. Then Nafion/PVPA blend membranes were prepared by means of film casting from Nafion/PVPA solutions with several molar ratios of PVPA repeat unit to - SO3H. Homogeneous Nafion/PVPA films were produced. Nafion-PVPA interactions were studied by Fourier transform infrared (FT-IR) spectroscopy. Thermal properties were investigated via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA results illustrated that all of these Nafion/PVPA electrolytes are thermally stable up to 400 degrees C. The membrane properties were further characterized by studying their morphologies using scanning electron microscopy (SEM). The proton conductivity of the Nafion/P(VPA)(3) blend membrane was 1.1x10(-5) S/cm in an anhydrous state at 130 degrees C. The conductivities of the blends increased by at least three orders of magnitude upon hydration, exceeding 10(-2) S/cm with RH=50 % at ambient temperature.