First-principles calculations were performed to determine the geometric structure and electronic states of Ni(110)-p2mg(2×1)-CO surface. We found that the CO molecules were adsorbed onto nearby short bridge sites. The molecular adsorption energy was calculated to be 1.753 eV. The C—O bond length was about 0.117 nm. The angle between the bond of the CO molecule and the vertical of the Ni(110) surface was 20.0°. The tilt angle of the direction linking the carbon and the center of the short bridge was 20.9°. The stretch vibration frequencies between the carbon and the oxide atoms of an adsorbed CO molecule was 1876 and 1803 cm-1. The density of states suggests that the chemical interaction between the CO molecules and Ni atoms was mainly caused by hybridization between molecular orbitals π, σ and d orbitals. Surface p2mg(2×1) reconstructionmay be attributed to the hybridization between σ molecular orbitals of CO and dxz orbitals of nickel atoms. Surface electronic states resulting from an interaction between σ molecular orbitals of CO and dxz orbitals of nickel atoms were localized below the Fermi energy (0 eV) from -10.4 to -8.8 eV and from -7.4 to -5.1 eV.