Background:　Chemical　sensors　that　work　as　electronic　noses　have　attracted　extensive　attention,　yet　research　about　sensor　application　of　C-doped　boron　nitride　nanotubes　is　still　rare.　Purpose:　In　order　to　realize　the　gas　sensing　properties　of　boron　nitride　nanotubes　(BNNTs)　and　C-doped　BNNTs　for　some　small　gas　molecules,　such　as　NO2,　O2　and　F2,　we　calculated　the　adsorption　property　of　those　gas　molecules.　Methods:　The　gas　sensing　properties　of　C-doped　BNNTs　for　some　small　gas　molecules　have　been　investigated　by　using　the　density　functional　theory.　Results:　The　interaction　distance　between　gas　molecule　and　BNNT　and　adsorption　energy　of　gas　molecule　on　the　BNNTs　and　the　C-doped　BNNTs　are　obtained　by　density　functional　theory　(DFT)　calculation.　We　also　calculated　the　electron　densities　of　states　for　an　O2　molecule　or　a　NO2　molecule　or　a　F2　molecule　to　adsorb　on　the　different　positions　of　C-doped　BNNTs.　Conclusion:　The　calculated　results　show　that　BNNTs　present　high　sensitivity　to　the　gaseous　NO2,　O2　and　F2　molecules.　The　chemical　reactivity　of　BNNTs　has　been　changed　by　carbon　molecules,　and　C-doped　BNNTs　can　improve　the　interaction　between　the　gas　molecules　and　the　BNNTs.　©　2016,　Science　Press.　All　right　reserved.