A new photocatalyst responsive to visible light was found in Zr-based oxynitrides derived from nitridation of ZrO2 in flowing NH3. Zr2ON2 with the bandgap of 2.6 eV functioned with irradiation of visible light, yielding H-2 and 02 by water reduction and oxidation in the presence of sacrificial reagents, respectively. The Zr2ON2 was stable during the photocatalytic reaction. Calculation of electronic structure for the Zr2ON2, based on plane-wave-based density functional theory (DFr), gave information that the main components of valence and conduction bands were the O 2p, N 2p and Zr 4d atomic orbitals, and no isolated band existed within the bandgap. In this paper, the visible-light photocatalytic properties of Zr2ON2 are discussed in terms of the electronic band structure calculated. (C) 2007 Elsevier B.V. All rights reserved.