The sol-gel method was applied to prepare the P2O5-TiO2-SiO2 glasses with high proton conductivities and chemical stability. The glasses were prepared by the reaction of the Ti- and Si-alkoxides with PO(OCH3)(3) or H3PO4, followed by heating at 600 degreesC. The obtained glasses were porous, the average pore diameter of which was < 2 and 4 nm for glasses prepared using PO(OCH3), and H3PO4, respectively. The phosphorous ions, occurring as PO(OH)(3) in the TiO2-free glass, were polymerized with one or two bridging-oxygen ions per PO4 unit with the increasing TiO2 content. Despite the P2O5-SiO2 binary glasses exhibiting high conductivities of similar to10(-2) S/cm at room temperature, they also dissolved after immersing for 24 h in water. The chemical stability of these glasses increased significantly on the addition of TiO2. (C) 2003 Elsevier B.V. All rights reserved.