Nitrogen-doped nanosized TiO2 powders were prepared by a simple thermal treatment method of the mixture of titanium dioxide and urea. The prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra (UV-Vis-DRS) and Fourier transform infrared (FT-IR) spectroscopy. The results showed that the crystal structure of N-TiO2 was a mixture of anatase and rutile phases, and the average particle size was 31 om calculated from XRD results. The UV-vis spectra indicate an increase in absorption of visible light when compared to undoped TiO2. The photocatalytic activity of nitrogen-doped TiO2 powder was evaluated by the decomposition of methylene blue under visible light irradiation. And it was found that nitrogen-doped TiO2 powders exhibited much higher photocatalytic activity than undoped TiO2. Moreover, the study also showed that, the doping N atoms improve the growth of the TiO2 crystal and phase transformation.