Various photocatalyst materials developed by the group of the author are described. Alkali and alkaline earth tantalates have arisen as a new group of photocatalyst materials for water splitting into H-2 and O-2 under ultraviolet light irradiation. They showed the activities even without co-catalysts such as Pt, being different from titanate photocatalysts. When NiO co-catalysts were loaded on the tantalate photocatalysts, the photocatalytic activities were drastically increased. Among the tantalates, NiO/NaTaO3 doped with La showed the highest activity. Some metal sulfide photocatalysts such as AgGaS2 and AgInZn7S9 showed high activities for H-2 evolution from aqueous solutions containing S2- and SO32- as electron donors under visible light irradiation (wavelength > 420 nm). The H-2 evolution was observed even under irradiation using a solar simulator. Pt/SrTiO3 doped with Rh has also arisen as a novel oxide photocatalyst for H-2 evolution from aqueous solutions containing reducing reagents under visible light irradiation. On the other hand, BiVO4 and AgNbO3 showed high activities for O-2 evolution in the presence of sacrificial reagent (Ag+) under visible light irradiation. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.