NaTaO3-xNx catalyst has been successfully synthesized from N-doped Ta2O5 precursors by a simple hydrothermal process. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. Density functional theory calculations suggested that the valence band of the catalysts was composed of the hybrid O 2p and N 2p orbitals, and the visible-light sensitivity is due to the narrowing of the band gap by mixing N 2p and O 2p states. NaTaO3-xNx catalyst could decompose the gaseous formaldehyde under the visible-light irradiation (lambda > 400 mn), and its photocatalytic activity depended on N dopant concentration. NaTaO2.943N0.047 showed the highest photoactivity for the formaldehyde photodegradation. (C) 2007 Elsevier Ltd. All rights reserved.