In this study, a new type of thiophene-based polybenzimidazole was synthesized by the condensation polymerization of 2,5-thiophene dicarboxylic acid and 3,3'-diaminobenzidine for high-temperature proton exchange membrane fuel cells. The resulting poly(benzimidazole-co-thiophene) (PBITH) membrane was prepared using the direct casting method at 200 A degrees C in a hot press. The PBITH membranes were immersed in a 10 mol phosphoric acid (PA) solution for 2 weeks. The proton conductivity of the doped-PBITH (DPBITH) membrane increased with increasing temperature, and the maximum conductivity was 0.120 S cm(-1) at 150 A degrees C and 15 % relative humidity. The DPBITH showed higher proton conductivity than the doped-polybenzimidazole membrane due to the presence of additional thiophene heterocycles. Incorporation of the thiophene groups as an additional sulfur containing heterocycle increased the basicity of the polymer backbone and enhanced the interaction between PA and the polymer. A novel thiophene-based polybenzimidazole membrane was synthesized through the condensation polymerization of 2,5-thiophene dicarboxylic acid and 3,3'-diaminobenzidine in phosphorous pentoxide/methanesulfonic acid solvent medium. The proton conductivity of the phosphoric acid-doped membrane was found to be 0.120 S cm(-1) at 150 A degrees C and 15 % relative humidity.