A novel single-step synthetic method for the preparation of anatase N-doped TiO2 nanocrystalline at low temperature has been devoleped. The N-doped anatase TiO2 nanoparticles were synthesized by sonication of the solution of tetraisopropyl titanium and urea in water and isopropyl alcohol at 80 degrees C for 150 min. The as-prepared sample was characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectrum. The product structure depends on the reaction temperature and reaction time. The photocatalytic activity of the as-prepared photocatalyst was evaluated via the photodegradation of an azo dye direct sky blue 5B. The results show that the N-doped TiO2 nanocrystalline prepared via sonication exhibit an excellent photocatalytic activity under UV light and simulated sunlight. (C) 2011 Elsevier Ltd. All rights reserved.