Water diffusion and its role on the proton conduction are discussed in the sol-gel-derived porous P2O5-SiO2 glasses. The diffusion coefficient of water in the glass is similar to 10(-7) cm(2)/s at room temperature. The electrical conductivity is proportional to the logarithm of the number of water molecules with three separate lines in response to the water concentration. The activation energy determined from the spin-lattice relaxation of proton is, similar to 10 kJ/mol, independent of the water concentration, whereas the activation energy for proton conduction decreases to similar to 10 kJ/mol with increasing water concentration.