Photocatalytic activities for the decomposition of distilled water into H2 and O2 were investigated on various tantalates. In the alkali and alkaline earth tantalates, LiTaO3, NaTaO3, KTaO3, MgTa2O6, and BaTa2O6 showed photocatalytic activities for water decomposition without co-catalysts. Among them, BaTa2O6 in the orthorhombic phase was the most active. The addition of a small amount of Ba(OH)2 into the water and supporting NiO drastically enhanced the photocatalytic reaction on the BaTa2O6 catalyst. On the other hand, in the transition metal tantalates, NiTa2O6 produced both H2 and O2 without co-catalysts.