Combined density functional theory and molecular dynamics simulations were performed to investigate ionic selectivity of boron nitride nanotubes (BNNTs). A finite-length (10, 10) BNNT with a diameter of 1.356 nm immersed in a reservoir of 1 M KCl solution can selectively conduct Cl ions, while K+ ions barely reach the center of the nanotube and do not conduct. In contrast, a (10, 10) single-walled carbon nanotube of approximately the same diameter immersed in a 1 M KCl solution can selectively conduct K+ ions through the nanotube. We investigate the potential of mean force analysis, binding energy calculations, the water structure, and its orientation, to explain the selectivity of BNNT. (C) 2009 Elsevier B. V. All rights reserved.