Ti02 sol—gel coatings, about 100 nm in thickness, were prepared by hydrolysis of Ti—alkoxides in alcoholic solutions and dip—coating. X—ray photoelectron spectra (XPS), thin film X—ray diffraction, dynamic microhardness (DH) and refractive indices of the coatings on silica glass substrates were measured after drying and heat treating at temperatures in the range from 100 to 900°C. The crystallization temperature of thin coatings was more than 100°C higher than that of the bulk gels. Ols spectra of XPS and the depth profile of the microhardness of the coatings show the structural changes in the depth direction in the coatings. The surface layer with high microhardness is considered to have an Anatase—like structure or to crystallize rapidly. The inner layer with relatively low microhardness contain a certain amount of water after heat treating at 500°C. Ols spectra of the inner layer near the surface of the substrate were different from those of the other parts of the coatings. Significant increase in the microhardness of the glass substrates was observed near the interface between the coating and the substrate was observed. This result suggests that stress in the surface layer of the substrate is induced by the coating. This result also shows good adhesion of the coatings on glass substrates. The structural changes of the coatings during drying and heat treating are also discussed.