Abstract: A series of high molecular mass sulfonated poly (imide-benzimidazole)s were synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA),6,6'-bis2-(4-aminophenyl)benzimidazole (BAPBI) and 3,3'-bis(4-sulfophenoxy)-benzidine (BSPOB) by high-temperature solution polycondenzation.Flexible membranes with improved mechanical strength,dimensional stability,hydrolytic and oxidative stability were prepared by the obtained polymers due to the introduction of the benzimidazole ring which could induce ionic cross-linking structure with sulfonic acid groups.The proton conductivity of membrane is 0.19 S/cm,which is higher than that of Nafion115 (0.13 S/cm).