Silver ions doping made enhancement of the photocatalytic activity of TiO2, which was determined by degradation of methyl orange (MO), a probe molecule, in an aqueous solution. X-ray diffraction (XRD) investigation demonstrated that the silver doping changed lattice parameters of TiO2, which should attribute to the O vacancies produced by the substitutional silver ion at lattice site. On above results, a doping mechanism of silver ions in TiO2 was also discussed. (C) 2003 Elsevier B.V. All rights reserved.