The Ir(111) surface is oxidized with gas-phase oxygen atoms under vacuum condition to achieve an oxidation level beyond its saturation coverage for chemisorption. Two surface oxides, rutile IrO 2 of (100) domain and corundum Ir 2 O 3 of (001) domain, have been grown at 550K with different oxygen exposure of 3.6×10 5 L and 7.2×10 5 L respectively. The temperature programmed desorption (TPD) experiment of rutile IrO 2 (100) shows its desorption curve (at 4Ks −1 ) peaks at 750K, followed by a long tail of less pronounced desorption features. On the other hand, TPD of corundum Ir 2 O 3 (001) displays a symmetric trace, peaking at 880K. Carbon monoxide titration experiments show that adsorbed CO reduces corundum Ir 2 O 3 (001) at 400K, but CO does not adsorb on rutile IrO 2 (100) and no reduction reaction occurs. Evidently, among the two surface oxides, corundum Ir 2 O 3 (001) involves in catalysis of carbon monoxide oxidation, while rutile IrO 2 (100) does not. The formation of two surface oxides is also compared, we conclude that the atom arrangement favors Ir 2 O 3 (001) at the oxide/metal interface.