The research on a new series of solid photocatalysts with different crystal structures was reviewed. The first system is A2B2O7 pyrochlore-crystal type: Bi2 MNb O7 (M=Al, Ga, In and Y, rare earth, and Fe), which is cubic system and space group Fd3m. The second system is ABO4 stibotantalite-crystal type: BiMO4 (M =Nb5+, Ta5+), in which both the triclinic system with space group P1 in the case of M=Ta and the orthorhombic system with space group Pnna in the case of M=Nb. The third system is ABO4 wolframite-crystal type: InMO4 (M=Nb5+, Ta5+), which is monoclinic system and space group P2/a. Although these photocatalysts crystallize in the different crystal structure, they contain the same octahedral TaO6 and/or NbO6 in the different photocatalysts. The band structure of the photocatalysts is defined by Ta/Nb d-level for a conduction band and O2p-level for a valence band. The band gaps of the photocatalysts were estimated to be between 2.7 and 2.4eV. Metal doped InTaO4 photocatalysts were also investigated. Under visible light (λ>420nm) or ultra-violet irradiation, the H2 and/or O2 evolutions were observed from pure water as well as aqueous CH3OH/H2O and AgNO3 solutions. The photocatalytic activity increases significantly by loading co-catalysts such as Pt, RuO2 and NiOx on the surface of the photocatalysts. Finally, direct water splitting into H2 and O2 under visible light irradiation was firstly established using newly synthesized NiOx (partly oxidized nickel) promoted In0.9 Ni0.1TaO4 photocatalyst.