The　possible　reaction　mechanisms　for　CO　oxidation　on　the　perfect　Cu2O(111)　surface　have　been　investigated　by　performing　periodic　density　functional　theoretical　calculations.　We　find　that　Cu2O(111)　is　able　to　facilitate　the　CO　oxidation　with　different　mechanisms.　Four　possible　mechanisms　are　explored　(denoted　as　M-ER1,　M-ER2,　M-LH1,　and　M-LH2,　respectively)　:　M-ER1　is　CO(gas)+O-2(ads)-＞　CO2(gas);　M-ER2　is　CO(gas)+O-2(ads)-＞　CO3(ads)-＞　O-(ads)+CO2(gas);　M-LH1　refers　to　CO(ads)+O-2(ads)-＞　O-(ads)+CO2(ads);　and　M-LH2　refers　to　CO(ads)+O-2(ads)-＞　OOCO(ads)-＞　O-(ads)　+CO2(ads).　Our　transition　state　calculations　clearly　reveal　that　M-ER1　and　M-LH2　are　both　viable;　but　M-ER1　mechanism　preferentially　operates,　in　which　only　a　moderate　energy　barrier　(60.22　kJ/mol)　needs　to　be　overcome.　When　CO　oxidation　takes　place　along　M-ER2　path,　it　is　facile　for　CO3　formation,　but　is　difficult　for　its　decomposition,　thereby　CO3　species　can　stably　exist　on　Cu2O(111).　Of　course,　the　reaction　of　CO　with　lattice　O　of　Cu2O(111)　is　also　considered.　However,　the　calculated　barrier　is　600.00　kJ/mol,　which　is　too　large　to　make　the　path　feasible.　So,　we　believe　that　on　Cu2O(111),　CO　reacts　with　adsorbed　O,　rather　than　lattice　O,　to　form　CO2.　This　is　different　from　the　usual　Mars-van　Krevene　mechanism.　The　present　results　enrich　our　understanding　of　the　catalytic　oxidation　of　CO　by　copper-based　and　metal-oxide　catalysts.　(C)　2010　American　Institute　of　Physics.　[doi:10.1063/1.3489663]