Nanocrystalline　In(OH)ySz　solid　solutions　were　synthesized　from　In(NOa)3　and　thiourea　in　an　aqueous　solution　of　ethylenediamine　via　a　facile　hydrothermal　method.　The　samples　were　characterized　by　X-ray　diffraction　(XRD),　Na-sorption　(BET　surface　area),　UV-vis　diffuse　reflectance　spectra　(DRS),　transmission　electron　microscopy　(TEM),　high-resolution　transmission　electron　microscopy　(HRTEM),　energy　dispersive　X-ray　spectra　(EDS),　and　X-ray　photoelectron　spectroscopy　(XPS).　The　position　of　the　valence　band　for　In(OH)ySz　was　established　by　ultraviolet　photoelectron　spectra　(UPS).　Electronic　band　calculations　based　on　density　functional　theory　(DFT)　revealed　that　upon　being　doped,　several　doping　states　derived　from　S　3p　orbitals　appeared　in　the　band　gap　of　undoped　In(OH)3.　In(OH)　ySz　showed　visible-light-driven　photocatalytic　activity　in　the　decomposition　of　gaseous　acetone.　A　possible　sub-band-transition　mechanism　of　the　photocatalysis　on　In(OH)ySz　solid　solutions　under　visible　light　irradiation　was　also　proposed　in　this　work.　©　2007　American　Chemical　Society.