A new sulfortated aromatic diacid, 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid (DSNDA), was prepared from 2,6-naphtlialenedicarboxylic acid by direct sulfonation. The chemical structure of the sulfortated monomer was characterized by FTIR, H-1 NMR, C-13 NMR and MS. A series of sulfonated polybenzimidazoles (sPBI-NF) were successfully synthesized from DSNDA, 2,2-bis(4-carboxyphenyl)hexafluoropropane and 3,3'-diaminobenzidine in poly(phosphoric acid). All the sulfortated samples having high-molecular-weights (M-n, 74,100-109,500) were soluble in some polar aprotic solvents such as DMF, DMSO and DMAc, and they could be easily formed into tough and flexible films via solution casting. The films presented good thermal stabilities (T-5% > 453 degrees C), high storage moduli and glass-transition temperatures (T-g > 220 degrees C), as well as tensile strengths of about 95 MPa and swelling degrees lower than 12%. The conductivity values of sPBI-NF60H measured at the temperature range from 30 to 90 degrees C vary from 5.7 x 10(-4) to 2.7 x 10(-3) S/cm at 100% relative humidity. (c) 2005 Elsevier B.V. All rights reserved.