Nitrogen monoxide (NO) has an unpaired electron in its 2π^* orbital, giving rise to various reactivity such as dissociation and dimerization on the surfaces. One of the most important and frequently discussed issues has been whether its unpaired electron survives or not when adsorbed on metal surfaces; NO on metal surfaces is an ideal model system to study the interaction between molecular spin moment and condensed matters. We investigate the valence states of NO molecules adsorbed on Cu(110) with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Two orthogonal 2π^* valence states are observed at the Fermi level, suggesting that the unpaired electron of NO is alive and localized on the molecule. The covalent interactions between two NO molecules are visualized by manipulating the overlap of their “active” 2π^* orbitals.