Photoinduced reaction in relations to water photolysis was studied on Pt- or other catalysts-supported TiO2 (P-25) particles. It was found that stoichiometric H-2 and O-2 formation does not take place with the photocatalyst, and only H-2 production was observed. A long-term water photolysis was carried out by Pt-supported TiO2 (TiO2/Pt) to produce H-2, in which H-2 formation stopped almost after 600 h irradiation. After recovering the TiO2/Pt particles used in the long-term reaction, they were reused in a photocatalytic H+ reduction by adding methanol as an electron donor, but no H-2 production was observed showing that the TiO2/Pt particles have lost their photocatalytic activity after the long-term reaction. These results suggest that TiO2 itself works as an electron donor to produce H-2 Structural change of the TiO2/Pt have been studied by both X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) before and after the photoreaction. In both the XRD and XPS, the structure of the original TiO2 almost disappeared after the photoreaction and new structures appeared, showing that Ti4+ changed irreversibly to a higher valance state (Ti5+) after producing H-2.