A novel sulfonated aromatic diacid, 3,3'-disulfonyl-4,4'-dicarboxyldiphenylsulfone (DSDCDPS), was successfully synthesized from 4,4'-dimethyldiphenylsulfone by sulfonation and further oxidation. A series of sulfonated polybenzimidazoles (sPBI-SS) with various sulfonation degrees was prepared from DSDCDPS, 4,4'-sulfonyldibenzoic acid and 3,3'-diaminobenzidine by solution copolycondensation in poly (phosphoric acid). The chemical structure of the resulting sPBI-SS was confirmed by FTIR and H-1 NMR. The DSDCDPS-based sPBI-SS with the number-average molecular weights of 32,000-55,000 were easy to dissolve in polar aprotic solvents such as DMF, DMSO, and DMAc, and could be cast into transparent, tough, and flexible membranes. The membranes presented good thermal stabilities (5% weight loss temperatures higher than 430 degrees C), and the thermal degradation activation energies of the sulfonic group of sPBI-SS40 evaluated under N-2 by both Ozawa and Kissinger methods were 266.06 and 264.79 kJ/mol, respectively. The membranes also exhibited high storage moduli, glass transition temperatures (above 238 degrees C) and tensile strengths (similar to 80 MPa), in addition to water uptakes (22.3-25.2%) and low swelling degrees (< 14.0%). (c) 2005 Wiley Periodicals, Inc.