Nanohybrid membrane of zirconia/polytetramethylene oxide synthesized by sol-gel processes was shown to possess flexible and temperature-tolerant properties. The polymeric membrane showed enhanced thermal stability up to 300 degreesC due to the presence of cross-linkable inorganic nanophase in the hybrid macromolecular matrix. The membrane becomes proton-conducting polymer electrolyte when added with 12-phosphotungstic acid (PWA) or soaked by phosphoric acid. The proton-conducting properties of the hybrid membranes with various PWA or phosphoric acid concentrations were investigated in the temperature range from room temperature to 150 degreesC under saturated humidity conditions. The flexible and large-sized hybrid polymer membrane has been found to have high proton conductivities from 1 x 10(-3) to 5 x 10(-2) S/cm under saturated humidity condition between 100 and 150 degreesC. (C) 2004 The Electrochemical Society.