First-principles calculations based on density functional theory (DFT) have been performed to investigate the adsorption of O-2 on the CaO and SrO (1 0 0) surfaces. The present results indicate that the bridge-top site for both the CaO and SrO (1 0 0) surfaces is the most favorable site for O-2 adsorption, with predicted adsorption energies of 1.437 eV and 1.236 eV, respectively. Detailed analysis of density of states, Mullikan population and vibration frequency are performed. The calculated results imply the possible formation of a peroxo (O-2(2-)) when O-2 is adsorbed with the bridge-top mode on both CaO and SrO (1 0 0) surfaces. (C) 2011 Elsevier B.V. All rights reserved.