Transport properties of NC3H quantum dot by adsorption of ammonia and carbon dioxide are investigated with an ab initio method combined with a non-equilibrium Green function method. The effects of different configurations of ammonia, size of NC3H surface and position where ammonia and carbon dioxide had been adsorbed onto NC3H quantum dot on transport properties are revealed. In comparison with NC3H quantum dot device, results show that the adsorption of ammonia molecule on NC3H quantum dot in one configuration enhances the conductance of device, while adsorption in another configuration reduces the conductance. The size of NC3H significantly altered the transport properties in both NC3H-NH3 and NC3H-CO2 system. The position of adsorption of ammonia displays obvious change on transport properties while the effects of position of carbon dioxide on transport properties are negligible. (C) 2015 Elsevier B.V. All rights reserved.