We studied adsorption of several molecules (CO, CO2, H2O, N2O, NO, NO2, and O-2) on hexagonal boron nitride (h-BN) monolayers supported on transition metal (TM) surfaces, using density functional calculations. We observed that all the molecules bind very weakly on the pristine h-BN, with binding energies in the range of 0.02-0.03 eV. Interestingly, however, when h-BN is supported on the TM surface, NO2 and O-2 become strongly chemisorbed on h-BN, with binding energies of > 1 eV, whereas other molecules still physisorbed, with binding energies of similar to 0.1 eV at most. The electron transfer from TM to p(z) states of h-BN played a substantial role in such strong bindings of NO2 and O-2 on h-BN, as these molecules possess unpaired electrons that can interact with p(z) states of h-BN. Such selective molecular binding on h-BN/TM originates from the peculiar distribution of the spin-polarized highest occupied and lowest unoccupied molecular orbitals of NO2 and O-2. Strong molecular adsorption and high selectivity would make the h-BN/TM system possible for a variety of applications such as catalysts and gas sensors. (C) 2013 Elsevier B. V. All rights reserved.