Equilibrium geometries, stabilities, and electronic properties of toxic CO and NO molecule adsorptions on the exterior surface of Al 12 N 12 nano-cage were investigated through density functional calculations. The obtained most stable adsorption configurations are those in which the C and N atoms of CO and NO are closed to an Al atom of the cluster, respectively, accompanied with the adsorption energies of −0.58 and −0.46eV. It was revealed that the electrical conductivity of the cluster may be increased upon the NO adsorption, being insensitive towards CO adsorption. Thus, the Al 12 N 12 cluster might selectively detect the NO molecule in the presence of CO molecules.