Proton-exchange membrane fuel cells (PEMFC)s are increasingly regarded as promising environmentally benign power sources. Heterocyclic molecules are commonly used in the proton conducting membranes as dopant or polymer side group due to their high proton transfer ability. In this study, 5-(methacrylamido)tetrazole monomer, prepared by the reaction of methacryloyl chloride with 5-aminotetrazole, was polymerized via conventional free radical mechanism to achieve poly(5-(methacrylamido)tetrazole) homopolymer. Novel composite membranes, SPSU-PMTetX, were successfully produced by incorporating sulfonated polysulfone (SPSU) into poly(5-(methacrylamido)tetrazole) (PMTet). The sulfonation of polysulfone was performed with trimethylsilyl chlorosulfonate and high degree of sulfonation (140%) was obtained. The homopolymers and composite membranes have been characterized by NMR, FTIR, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). H-1-NMR and FTIR confirmed the sulfonation of PSU and the ionic interaction between sulfonic acid and poly(5-(methacrylamido)tetrazole) units. TGA showed that the polymer electrolyte membranes are thermally stable up to approximate to 190 degrees C. Scanning electron microscopy analysis indicated the homogeneity of the membranes. This result was also supported by the appearance of a single T-g in the DSC curves of the blends. Water uptake and proton conductivity measurements were, as well, carried out. Methanol permeability measurements showed that the composite membranes have similar methanol permeability values with Nafion 112. The maximum proton conductivity of anhydrous SPSU-PMTet0.5 at 150 degrees C was determined as 2.2 x 10(-6) S cm(-1) while in humidified conditions at 20 degrees C a value of 6 x 10(-3) S cm(-1) was found for SPSU-PMTet2. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40107.