In this study, the adsorption of carbon monoxide (CO) gas, on the surface of boron nitride nanotubes in pure form, as well as doped with Al and Ga, based on the density functional theory has been studied. The electron and structural properties of pristine and doped nanotubes have been investigated. By calculating the adsorption energy, the most stable positions and the equilibrium distance are obtained, and charge transferred and electron properties have been calculated. The most stable molecule adsorption position for pure nanotube is obtained at the center of the hexagon and for doped nanotube above the impurity. Adsorption of the molecule that is perpendicular to the nanotube axis is more stable than that with the horizontal position to the nanotube axis, and the adsorption from C atoms side is stronger than O atoms. According to the results, zigzag boron nitride nanotube is more sensitive to the adsorption of CO molecules than armchair type. The results show that gas molecule adsorption has a very slight effect on the electrical properties of pure nanotubes, which can indicate a physical adsorption. After doping, the amount of adsorption energy has changed for the most stable positions and shifted to the range of chemical adsorptions. (C) 2018 Elsevier B.V. All rights reserved.