LaTiO2N, a Ti-based oxynitride, was studied as a visible-light (420-600 nm)-driven photocatalyst. DFT calculation for LaTiO2N indicated that the top of the valence band consists predominantly of N 2p orbitals with a small contribution by O 2p orbitals, while the bottom of the conduction band is made up entirely of empty Ti 3d orbitals. LaTiO2N was synthesized from a La2Ti2O7 precursor at 1123 K under NH3 flow. The relationship between the preparation condition and the photocatalytic activities of H+ reduction to H-2 and H2O oxidation to O-2 was examined. It was found that the photocatalytic activity for O-2 evolution increased with nitridation time, reaching a maximum at 72 h. Further treatment beyond 72 h lowered the rate of O-2 evolution. The rate of H-2 evolution was almost independent of nitridation time. The relationship between nitridation time and the rate of O-2 evolution is discussed on the basis of X-ray photoelectron spectroscopy (XPS) analyses.