The coadsorption of Na and CO on Ni (111) at room temperature was investigated using high-resolution electron energy loss spectroscopy. A notable softening of the Na-Ni bond was revealed in the Na+ CO coadsorption phase. A lengthening of the Na-Ni bond was observed upon annealing the substrate. Oxygen adsorption on Na+ CO/Ni (111) caused a significant blue-shift of the C-O stretching frequency. Exposing the Na/Ni (111) to oxygen, no Na-O bond was observed. On the contrary, the formation of the Na-O bond was easily achieved by exposing the Na+ CO/Ni (111) phase to oxygen.