Abstract: Fluorine-doped TiO₂ sol(F-TiO₂) was prepared by the modified precipitation-sol-hydrothermal crystallization method with TiCl4 as precursor.The influences of F doping, temperature and time of hydrothermal crystallization, medium pH value on the morphology and crystallization were studied.The particle size and structure of the prepared F-TiO₂ sol as well as the interaction of F with TiO₂ were characterized with XRD, UV-Vis-DRS, TEM, TG-DTA, FTIR and XPS.The results showed that F-TiO₂ particles in sol were spherical, and partly crystallized to anatase.They were dispersed in the aqueous medium uniformly and showed narrow particle size distribution.The average particle size was 6.5 nm as calculated from XRD and TEM results.It was also shown that fluorine atoms were adsorbed by TiO₂ sol particles in two forms.One was physically adsorbed on the surface of TiO₂, and the other was embedded into TiO₂ crystal lattice.It was found that the addition of fluorine could improve the crystallization of particle significantly, decrease the temperature and shorten the time of hydrothermal crystallization.The adsorption capacity, surface acidity and the photocatalytic activity for decomposition of Rhodamine B were enhanced remarkably with the doping of fluorine.The mechanism of improvement of the photocatalytic activity and structure of TiO₂ by fluorine was discussed.