Surface modification of a boron nitride nanotube (BNNT) with sulfamide molecule has been investigated in terms of its energetic, geometric, and electronic properties using B3LYP and PBE density functionals. The sulfamide molecule can be physically adsorbed on the tube surface or chemically diffuse into its wall, accompanied by the release of one NH3 molecule. Calculated density of states show that the electronic properties of the BNNT are slightly changed upon the chemical modification. Accordingly, HOMO-LUMO energy gap of the tube is changed by about -4.8 to +10.5%, predicted using the B3LYP functional with 6-31G (d) basis set. Moreover, the work function is slightly decreased which may facilitate the field electron emission from the BNNT surface. Preservation of the electronic properties of the BNNT coupled with the enhanced solubility suggests that chemical modification of the BNNTs with sulfamide may be an effective way for their purification. (c) 2012 Elsevier B.V. All rights reserved.