In this paper, TiO2 sol was prepared by chemical coprecipitation-peptization method. XRD pattern shows that TiO2 sol particles without calcination treatment had anatase crystal structure. The particle size distribution (PSD) analysis shows that TiO2 sol particles had narrow distribution characterization with a mean size of 21 nm, which was in good agreement with analytical result by AFM (25 nm). A novel hydrosol reaction system was applied to process X-3B photodegradation reaction under visible light illumination. The results demonstrate that TiO2 sol nanoparticles have better interfacial adsorption capability and higher photoactivity than P25 TiO2 in suspension system, which was ascribed to the characteristics of better dispersion, less aggregation of composite TiO2 sol nanoparticles in the aqueous medium. By adjusting the pH value of hydrosol system, TiO2 sol nanoparticles can be effectively separated front X-3B/TiO2 hydrosol reaction system and dispersed again into aqueous solution to form sol system. This TiO2 sol photocatalyst can be applied to recycle use for many times while keeping high photoactivity on X-3B degradation reaction. (C) 2003 Elsevier B.V. All rights reserved.