Influences of humidity and temperature on the weathering of soda-lime-silica glass substrates coated with sol-gel derived TiO2-SiO2 and pure SiO2 films have been studied, and the weathering mechanism of the glass substrates has been discussed. The weathering of glass substrates coated with the films was drastically accelerated with increasing humidity and with increasing temperature in the environment. The weathering of the glass substrates coated with sol-gel derived films proceeded by the ion exchange of hydronium ions (or protons) from atmosphere with sodium ions in the glass substrates and by the subsequent reactions of the sodium ions with carbondioxide and water in the atmosphere on the surface of the coating films. It was found that the sol-gel derived TiO2-SiO2 coating films provide the substrates with better durability in the environment of high temperature and high humidity compared with the pure SiO2 coating films. The apparent activation energy for the weathering of the glass substrates coated with the 9TiO2⋅91SiO2 (in mol%) films was estimated to be 68kJ·mol-1 under 90% R. H.