N-I co-doped TiO2 nanoparticles were prepared by hydrolysis method, using ammonia and iodic acid as the doping sources and Ti(OBu)(4) as the titanium source. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS). XRD spectra show that N-I-TiO2 samples calcined at 673 K for 3 h are of anatase structure. XPS analysis of N-I-TiO2 samples indicates that some N atoms replace O atoms in TiO2 lattice, and I exist in I7+, I- and I5+ chemical states in the samples. UV-vis DRS results reveal that N-I-TiO2 had significant optical absorption in the region of 400-600 nm. The photocatalytic activity of catalysts was evaluated by monitoring the photocatalytic degradation of methyl orange (MO) Compared with P25 and mono. doped TiO2, N-I-TiO2 powder shows higher photocatalytic activity under both visible-light (lambda > 420 nm) and UV-vis light irradiation. Furthermore, N-I-TiO2 also displays higher COD removal rate under UV-vis light irradiation. (C) 2009 Elsevier B.V. All rights reserved.