Cerium and nitrogen co-doped anatase TiO2 nanoparticles were synthesized using a one-step technique via a modified sol-gel process and characterized by XRD, BET, DRS, Raman and XPS. The photocatalytic mechanism of the degradation of methylene blue (MB) under fluorescent light and visible light irradiation was studied. Co-doping cerium and nitrogen in the crystal lattice of TiO2 narrowed the band gap from 2.40 eV (Ce-doped TiO2) to 2.21 eV (Ce/N co-doped TiO2). Ce4+/Ce3+ pairs, oxynitride species and Ti-O-N and Ti-O-Ce bonds were determined by XPS. The recombination of photogenerated electron-hole pairs was inhibited due to the synergistic effect of doping with Ce4+/Ce3+ ions and N atoms. The optimal doping ratio was 0.70% Ce and 0.70% N using MB photocatalytic degradation under fluorescent light and visible light irradiation (lambda > 420 nm). The enhanced photocatalytic degradation under visible light irradiation was attributed to the increasing number of photogenerated center dot OH radicals. The recombination of photogenerated e(-)-h(+) was attributed to be the key factor for the decrease in the photocatalytic degradation efficiency of MB. (C) 2009 Elsevier B.V. All rights reserved.