Structure and crystal grain size distribution along the thickness of TiO2/SiO2 thin films prepared by the sol-gel process under various heating temperatures were studied. The X-ray diffraction spectra indicated that the crystalline forms of TiO2 in the film depend on the TiO2, content. The phase transformation kinetics depend on the anatase particle size. X-ray grazing incidence analyses indicated that the crystal size decreases along the thickness of the thin film. Increasing the heat-treatment temperature increased the difference in crystal size along the depth of thin film. (C) 1999 Elsevier Science B.V. All rights reserved.