The　reaction　mechanisms　for　CO　catalytic　oxidation　by　N2O　or　O2　on　the　Co3O4　(110)　surface　were　studied　by　DFT　slab　calculations.　CO　chemisorbs　preferably　at　a　surface　Co3+　site.　After　the　Co3+　site　is　completely　covered,　CO　adsorbs　at　the　neighboring　twofold　coordinated　surface　oxygen　atom　bonded　to　Co2+　and　Co3+　cations,　resulting　in　the　formation　of　CO2　and　an　oxygen　vacancy　with　a　low　energy　barrier　of　0.033　eV,　which　rationalizes　the　experimental　observation　that　Co3O4-based　systems　are　active　for　CO　oxidation　at　low　temperatures.　N2O　or　O2　interacts　with　the　oxygen　vacancy　site　to　regenerate　the　surface,　leaving　N　2　or　the　activated　O2　-　species　to　be　attacked　by　the　second　CO　to　yield　CO2　to　proceed　with　the　catalytic　cycle.　The　CO　oxidation　reaction　follows　the　Mars-van　Krevelen　mechanism.　©　2009　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim.