We investigated the relation among the bulk crystal structure, the related electronic properties, photophysical behavior and the photocatalytic activity on oxide photocatalyst InMO4 (M=4d-Nb and 5d-Ta) by light absorption measured, the first principle calculations as well as water splitting experimental results. These oxide photocatalysts crystallize in the same crystal structure: wolframite type, monoclinic with space group P2/a. However, the octahedral TaO6 in InTaO4 slightly expands from that of NbO6 in InNbO4, leading to the longer lattice parameters in InTaO4. Under visible light irradiation (lambda>420nm), the oxide photocatalysts were found to evolve H-2 from water. The band gaps of InTaO4 and InNbO4 were estimated to be 2.6 and 2.5 eV, respectively. The slight difference in the band gaps of the two photocatalysts is due to their different conduction band levels formed by 5d-Ta in TaO6 and 4d-Nb in NbO6, resulting in little difference in photocatalytic activity of the two photocatalysts.