A　series　of　polyaniline–titanium　dioxide　(PANI/TiO2)　nanocomposite　film　sensor　were　fabricated　by　an　in-situ　chemical　oxidation　polymerization　of　aniline　at　TiO2　(anatase)　surface,　and　were　evaluated　the　CO　gas　sensitivity　under　UV　irradiation　at　room　temperature.　Although　adding　PANI　into　TiO2　seemed　to　weaken　the　photo-assisted　conductivity　of　film　sensor　sample　at　N2　atmosphere,　it　enhanced　the　photo-assisted　gas　sensitivity　to　CO.　Based　on　the　chemical　characterization　results　of　PANI/TiO2　by　FT-IR,　Raman　and　XPS,　it　is　proposed　that　the　protonated　N　site　in　PANI　chains　(formed　by　TiO2　interacting　with　PANI)　would　promote　the　adsorption　of　CO,　resulting　in　the　more　electrons　from　CO　to　PANI　by　the　typical　π–conjugated　structures　of　benzenoid　and　quinonoid　units　and　then　to　TiO2　by　the　hydrogen　bonds　(N⋯H⋯O)　in　the　interface　of　PANI　and　TiO2.　Moreover,　the　presence　of　H2O　could　enhance　this　photo-assisted　gas　sensitivity.　Furthermore,　the　PANI/TiO2　powder　sample　also　exhibited　a　higher　activity　of　photocatalytic　oxidizing　CO　than　the　pure　TiO2　sample,　indicating　that　the　enhancement　in　the　photo-assisted　sensing　response　to　CO　would　benefit　the　photocatalytic　oxidation　of　CO　over　PANI/TiO2.　This　study　not　only　provides　a　possible　approach　to　develop　a　photo-assisted　gas-sensitive　material　by　introducing　the　structure　of　organic-inorganic　hybrided　nanocomposite,　but　also　provides　a　possible　method　to　estimate　the　photocatalytic　activity　of　a　semiconductor　material　by　testing　its　photo-assisted　sensitivity　to　the　reactant　gas.　©　2017　Elsevier　B.V.