Zn-doped TiO2 nanoparticles with high photocatalytic activity were synthesized by the hydrogen-oxygen diffusion flame method and the photocatalytic degradation mechanism of rhodamine B dye under visible light irradiation were elaborated. The Zn dopants presented in the form of small ZnO nuclei dispersing randomly on the surface of anatase TiO2 nanoparticles. It is found that the photosensitized degradation activity can be enhanced by doping an appropriate amount of Zn. The improved activity by Zn doping can be attributed to the appropriate energetic position between ZnO and the excited state of dye, which enhanced the electron injection into the conduction band of TiO2 by capturing electron, subsequently promoted the formation of reactive oxygen species. Hence, the enhanced photodegradation of dyes under visible irradiation can be realized. (C) 2007 Elsevier B.V. All rights reserved.