A new photocatalytic reaction that splits water into H-2 and O-2 was designed by a two-step photoexcitation system composed of a IO3-/I-shuttle redox mediator and two different TiO2 photocatalysts, Pt-loaded TiO2-anatase for H-2 evolution and TiO2-rutile for O-2 evolution. Simultaneous gas evolution of H-2(180 mu mol/h) and O-2(90 mu mol/h) was observed from a basic (pH = 11) NaI aqueous suspension of two different TiO2 photocatalysts under UV irradiation (lambda > 300 =, 400 W high-pressure Hg lamp).