The adsorption of CO molecule on the Cu2O (1 1 1) surface with or without pre-adsorbed oxygen atom (O-ad) has been investigated using density functional theory calculation. Calculations show that the adsorption of O-ad causes obvious changes in the electronic structure and charge distribution of Cu2O with a charge transfer of 0.48 e from substrate to O-ad. On the perfect Cu2O (1 1 1) surface, the one-fold coordinated copper (Cu-1c) atom is the most favorable site for the adsorption of CO with a charge transfer of 0.414 e from CO molecule to substrate. Moreover, it is found that the adsorption of CO on the O pre-adsorbed Cu2O (1 1 1) surface is strengthened. The adsorbed CO molecule tends to interact with O-ad atom and release the electrons trapped by the oxygen adatom back to the substrate, resulting in a significant charge variation (0.619 e). All these findings indicate that Cu2O would be a good candidate for the detection of CO gas. (C) 2013 Elsevier B.V. All rights reserved.