High proton conducting P2O5-SiO2 glasses were prepared using the sol-gel method, the electrical conductivities of which were studied in relation to the pore structure and the adsorbed water. The pore properties of SiO2 and P2O5-SiO2 glasses were controlled by addition of formamide during the gel synthesis, the specific surface areas of which were changed from 200 to 900 m(2)/g-glass. These glasses absorb water molecules on exposure to a humid atmosphere. The conductivity increased with increasing logarithm of water concentration and reached a saturated value above the water vapor pressure of 0.8. The highest conductivity, 2 x 10(-2) S/cm at room temperature, was achieved by 5P(2)O(5)-95SiO(2) glass heated at 700 degrees C and absorbing the water molecules.