Abstract.A proton-exchange membrane for a direct methanol fuel cell was prepared by modifying the chemical structure of poly(vinyl alcohol) (PVA) by means of sulfonation. We report the synthesis of a new proton-conducting polymer membrane with poly (vinyl alcohol) and diamine-containing organic molecules immobilized to PVA. The sulfonation was carried out by using 4,4-diaminodiphenyl ether-2,2-disulfonic acid (ODADS). A sulfonated diamine monomer, ODADS, was successfully synthesized by direct sulfonation of a commercially available diamine, 4,4-diaminodiphenyl ether (ODA), using fuming sulfuric acid as the sulfonating reagent. The chemical structure and thermal stability of the sulfonated PVA were studied by using FTIR and thermogravimetric analysis techniques, respectively. The proton conductivities of membranes were investigated as a function of ODADS content. The thermal decomposition of PVA-ODADS membranes started at 220°C. Differential scanning calorimetry (DSC) results indicated the homogeneity of the blends. Proton conductivity values of the sulfonated PVA membranes ranged between 8.25 and 16.53 mS/cm and the conductivities of PVA-ODADS membranes increased with the increasing ODADS content.