Periodic　density　functional　theory　calculations　using　pseudopotential　plane-waves　were　performed　systematically　to　investigate　the　surface　relaxation　of　different　Al2O3　surfaces　including　alpha-Al2O3　(0001)　and　gamma-Al2O3　(110),　(110C),　and　(110D)　surfaces,　as　well　as　the　adsorption　of　CO　molecules　on　these　surfaces.　Our　calculated　results　indicate　that　the　CO　molecules　tend　to　adsorb　perpendicularly　on　the　Al　atoms　at　the　surface　through　carbon　atoms　and　interactions　were　observed　between　the　CO　5　sigma　state　and　the　substrate.　After　adsorption,　some　electrons　transferred　from　the　CO　molecules　to　the　surface　and　accordingly　the　surface　work　functions　of　the　different　Al2O3　surfaces　decreased.　The　adsorption　results　in　small　perturbations　of　the　C　-　O　bond　length　and　the　corresponding　C　-　O　stretching　frequency　was　blue-shifted　in　all　the　adsorption　structures.　By　examining　the　results　of　the　CO　adsorption　on　the　different　surfaces,　it　is　clear　that　CO　can　be　used　as　an　effective　probe　molecule　to　distinguish　the　active　adsorption　sites　on　the　different　Al2O3　surfaces.