The behavior of the thiocyanate anion (SCN -) adsorbed on the external surface of H-capped (6,0), (7,0), (8,0), and Ga-doped (6,0) zigzag single-walled boron nitride nanotubes was studied by using density functional calculations. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 suite of programs. We present the nature of the SCN -interaction in selected sites of the nanotubes. Our results show that the pristine boron nitride nanotubes cannot significantly detect SCN -. The calculated binding energy of the Ga-doped (6,0) single-walled boron nitride nanotube indicated that SCNcan be absorbed significantly on the Ga site and these nanotubes can therefore be used for SCN -storage. Binding energy corresponding to adsorption of SCN -on the Ga site in the Ga-doped (6,0) single-walled boron nitride nanotube was calculated to be -263.3 kJ mol -1 . The calculated binding energies for SCN -in N-down orientation are higher than those in S-down orientation for all of the configurations. Also, we showed that the nanotube diameter has no significant role in determining the binding energy of SCN -and only the orientation and location of the SCNand also doping of nanotubes by other atoms play an important role in determining the binding energy. The decrease in global hardness, energy gap, and ionization potential due to SCN -adsorption leads to a the lowering of stability and increase in reactivity of the (6,0) zigzag SCN --and Ga-doped (6,0) zigzag SCN --boron nitride nanotube complexes.