Poly(5-vinyltetrazole-co-acrylonitrile) (P(VT-co-AN)) with different molecular weight and tetrazole content was synthesized from polyacrylonitrile. The chemical structures of the copolymers were characterized by FT-IR, H NMR spectroscopy and elemental analysis. The surface structure of the copolymer was characterized by scanning electron microscopy (SEM). Membranes of these polymers were prepared and the effect of molecular weight, tetrazole content, and acid doping level on the proton conductivity of phosphoric acid doped P(VT-co-AN) membranes was studied. The membranes with lower molecular weight, higher tetrazole content, or higher acid doping level show the higher proton conductivity. The temperature dependence of the proton conductivity of the acid doped membranes can be fitted by a simple Arrhenius equation either below or above the glass transition temperature of the copolymer. P(VT-co-AN) (Mn = 80,000)/1.0H(3)PO(4) can exhibit an anhydrous proton conductivity of 10(-4) S cm(-1) at room temperature and the proton conductivity increases with increasing temperature and acid doping level. (C) 2005 Elsevier B.V. All rights reserved.