Multivalency　iodine　(J7+/I-)　doped　TiO2　were　prepared　via　a　combination　of　deposition-precipitation　process　and　hydrothermal　treatment.　The　as-prepared　samples　were　characterized　by　X-ray　diffraction,　transmission　electron　microscopy,　Brunauer-Emmett-Teller　surface　area,　UV-vis　diffuse　reflectance　spectra,　X-ray　photoelectron　spectroscopy,　surface　photovoltage　spectroscopy,　and　electric-field-induced　surface　photovoltage　spectroscopy.　The　electronic　structure　calculations　based　on　the　density　functional　theory　revealed　that　upon　doping,　new　states　that　originated　from　the　I　atom　of　the　IO4　group　are　observed　near　the　conduction-band　bottom　region　of　TiO2,　and　the　excitation　from　the　valence　band　of　TiO2　to　the　surface　IO4　is　responsible　for　the　visible-light　response　of　the　I-doped　TiO2.　The　as-prepared　I-doped　TiO2　showed　high　efficiency　for　the　photocatalytic　decomposition　of　gaseous　acetone　under　visible　light　irradiation　(λ　＞　420　nm).　A　possible　mechanism　for　the　photocatalysis　on　this　multivalency　iodine　(i7+/I-)　doped　TiO2　under　visible　light　was　also　proposed.　©　2008　American　Chemical　Society.