Photochemical reactions on LaTiO2N, a perovskite-type oxynitride, were examined, Under visible-light irradiation (420 nm < lambda < 600 nm), LaTiO2N reduced H+ into H-2 and oxidized H2O into O-2 in the presence of a sacrificial electron donor (methanol) or acceptor (Ag+) by the band gap transition (2.1 eV). Oxidation of water proceeded with little degradation of the oxynitride, whereas partial substitution of Ca2+ for La3+ of LaTiO2N and modification by IrO2 colloid markedly suppressed degradation of the oxynitride and increased O-2 evolution efficiency.