The　adsorption　and　reactivity　of　O2　on　perfect　and　defective　(10,　0)　boron　nitride　nanotubes　(BNNTs)　are　investigated　employing　the　density-functional　theory.　Our　results　indicate　that　O2　prefers　to　physically　adsorb　on　perfect　BNNT.　The　assumed　dissociation　of　O2　on　the　perfect　BNNT　is　endothermic　and　difficult　to　realize　with　an　energy　barrier　of　3.25　eV.　The　point　defects　such　as　vacancies　and　Stone-wales　defect　on　the　wall　of　BN　nanotubes　reduce　the　oxidation　resistance　of　the　tubes.　Especially,　O2　is　dissociated　on　nitrogen　vacancy　tube　with　a　barrier　of　0.84　eV.　The　electronic　properties　analysis　indicates　that　chemisorbed　O2　can　reduce　the　energy-gap　of　BN　tubes.　©　2007　Elsevier　B.V.　All　rights　reserved.