Visible-light responsive N-doped ZrO2/TiO2 photocatalysts were synthesized via a sol-gel process. To obtain the optimum nitrogen doping content and operational conditions for photodegradation of NO, several key factors (including nitrogen doping, initial NO concentration, light intensity, reactor temperature, etc.) were investigated under both UV and visible light irradiation. Physical characterization of the photocatalysts was performed using X-ray diffraction (XRD), UV-visible absorption spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). The observed results suggest that nitrogen was doped in the lattice of TiO2 and had an effect on the translation of phase, photodegradation activity, and visible-light response. Among synthesized photocatalysts, 0.1 M Zr and 0.15 M N supported on TiO2 exhibited the best visible-light response and the highest NO photodegradation activity. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.