By means of X-ray diffraction, BET nitrogen adsorption, UV-Vis-NIR transmission spectroscopy, transmission electron microscope, scanning electron microscope, X-ray photoelectron spectroscopy and photodegradation of methylene blue, effects of Ag doping on the microstructure and photocatalytic activity of TiO2 films prepared by sol-gel method were studied. It is found that with a suitable amount (2-4 mol%), the Ag dopant increases the photocatalytic activity of TiO2 films. The mechanism can be attributed to that (1) anatase grain sizes decrease with Ag doping and the specific surface areas of doped TiO2 films increase, the charge transfer in TiO2 films is promoted; (2) by enhancing the electron-hole pairs separation and inhibiting their recombination, the Ag dopant enhances the charge pair separation efficiency for doped TiO2 films. (C) 2002 Elsevier Science B.V. All rights reserved.