New photocatalysts MIn0.5Nb0.5O3 (M = Ca, Sr, and Ba) with the ABO(3) type perovskite structure in which B sites are occupied by In3+ or Nb5+ ions randomly in a charge-balanced manner were synthesized. They were characterized by structural analysis, diffuse reflectance spectroscopy, and photocatalytic activity measurement in evolving H-2 and O-2 from pure water with cocatalysts Pt and NiOx under UV and visible light irradiation (lambda > 420 nm), respectively. It is suggested that the conduction bands of these photocatalysts are composed of In 5s and Nb 4d levels, and the valence bands are composed of O 2p levels. With the decrease of the ionic radius in the A site, the CaIn0.5Nb0.5O3, SrIn0.5Nb0.5O3, and BaIn0.5N0.5O3 photocatalysts show different photocatalytic activities. Under UV light irradiation, the BaIn0.5Nb0.5O3 photocatalyst powder with cocatalyst NiOx split pure water into H-2 and O-2 in a nearly stoichiometric ratio. Under visible irradiation, all of these photocatalysts show obvious photocatalytic activity in evolving H-2 from pure water with cocatalyst NiOx.