The　photoconductivity　and　the　gas　sensing　property　of　TiO2　at　room　temperature　under　ultraviolet　(UV)　irradiation　were　compared　with　those　under　visible　light　irradiation　(＞=　420　nm),　respectively.　It　was　found　that　UV　light　could　cause　the　photoconductivity　of　TiO2　and　its　sensing　response　to　both　ethylene　and　oxygen,　while　the　visible　light　at　420　nm　could　cause　the　photoconductivity　of　TiO2　and　its　sensing　response　to　oxygen　but　not　to　ethylene.　This　indicates　that　the　photo-assisted　gas　sensing　performance　of　TiO2　was　dependent　on　its　light-excited　behavior:　The　intrinsic　excitation　of　TiO2　induced　by　UV　light　could　produce　both　the　holes　and　electrons,　which　exhibited　a　respective　response　to　ethylene　and　oxygen,　while　the　extrinsic　excitation　of　TiO2　induced　by　visible　light　maybe　only　produced　the　free　electrons　but　not　free　holes,　resulting　in　only　a　response　to　oxygen.　Furthermore,　it　was　found　that　the　visible-light　enhanced　conductivity　maybe　depend　on　the　Ti-bonded　hydroxyls　(Ti-OH)　at　TiO2　surface.　With　the　removal　of　Ti-OH　by　increasing　temperature,　the　visible　light　could　not　produce　the　photoconductivity　of　TiO2.　It　was　proposed　that　Ti-OH　groups　act　as　the　shallow　trapped　level　to　cause　the　extrinsic　excitation　of　TiO2.　(C)　2017　Elsevier　B.V.　All　rights　reserved.