This study examined the adsorption of CO on a Mo(110) surface by Thermal Desorption Spectroscopy (TDS) and synchrotron-radiation based photoemission spectroscopy (SRPES). CO desorption was observed at approximately 400 K ($alpha$-CO) and > 900 K ($eta$-CO). When CO was exposed to Mo(110) at 100 K, it showed a tilted structure at low CO coverage and a vertical structure after saturation of the tilted CO. After heating the CO-precovered sample to 900 K, a broad peak at 12 eV below the Fermi level was identified in the valence level spectra, which was assigned to either the 4$sigma$-molecular orbital of CO, or 2s of dissociated carbon. TDS results of the $eta$-CO showed a first order desorption. These results are in a good agreement with the observations of CO adsorption on W(110) surfaces.