The adsorption and reactivity Of O-2 on perfect and defective (10, 0) boron nitride nanotubes (BNNTs) are investigated employing the density-functional theory. Our results indicate that O-2 prefers to physically adsorb on perfect BNNT. The assumed dissociation of O-2 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, O-2 is dissociated on nitrogen vacancy tube with a barrier of 0.84 eV. The electronic properties analysis indicates that chemisorbed O-2 can reduce the energy-gap of BN tubes. (c) 2007 Elsevier BN. All rights reserved.