Multivalency iodine (I7+/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 is responsible for the visible-light response of the I-doped excitation from the valence band of TiO2 to the surface 104 TiO2. The as-prepared I-doped TiO2 showed high efficiency for the photocatalytic decomposition of gaseous acetone under visible light irradiation (lambda > 420 nm). A possible mechanism for the photocatalysis on this multivalency iodine (I7+/I-) doped TiO2 under visible light was also proposed.