The adsorption properties of first-row atoms on zigzag single-walled boron nitride nanotubes (BNNTs) are studied using density functional theory. An interesting selectivity of adsorption is observed: the adsorption energy and adsorption site are dependent upon the chemical activity of adsorbate with respect to the B and N atoms in the host tube, which can be explained with the frontier molecular orbital theory. The mechanism of modification of electronic properties of BNNTs by atomic adsorption is demonstrated. In addition, it is found that the adsorption energies increase with increasing tube curvature, especially under large tube curvature. (c) 2006 Elsevier B.V. All rights reserved.