The adsorption of CO, CO2, NO and CO2 gas molecules on different chiralities of single boron nitride nanotubes (BNNTs) is investigated, applying the density functional theory and using basis set 6-31 g (d,p). The energetic, electronic properties and surface reactivity have been discussed. We found that the best BNNT for adsorbing the CO, CO2, NO and NO2 gas molecules is (5,0) BNNT with adsorption energy of −0.27, −0.37 eV, −0.23 and-0.92 eV, respectively. Also, the electronic character of (5,0), (9,0), (5,5) and (6,6) BNNTs is found to be not affected by the adsorption of CO, CO2, NO and NO2 gas molecules. It is found that the dipole moments of zigzag (5,0) and (9,0) BNNTs are always higher than the armchair (5,5) and (6,6) BNNTs. Also, it is noticed that the highest dipole moment is for (9,0) BNNT.