Abstract: 3,3′-Disulfonate-4,4′-dimethyl biphenyldicarboxylate (SMPC) and bis(4-methyl benzoate)phenyl phosphine oxide (MBPO) were synthesized by esterification. Subsequently, soluble sulfonated polybenzimidazoles with triphenyl phosphine oxide groups were prepared by polycondensation of SMPC and MBPO with 3,3′-diaminobenzidine in order to improve the solubility and proton conductivity of the product. The phenyl pendant groups of triphenyl phosphine oxide moieties made the polymer backbone to arrange loosely and thus endowed the product with good solubility. Moreover, phosphine oxide groups enhanced the water uptake of the products and greatly improved their proton conductivity.