We observed four kinds of adsorbed NO molecules on Pt(997) at 11K using infrared reflection absorption spectroscopy (IRAS). The peaks at 1690, 1484 and 1615cm −1 are assigned to the N–O stretching modes of the on-top site and the hollow site on the terrace and the bridge site at the step, respectively. The 1385cm −1 peak is observed below ∼70K. We assign the 1385cm −1 peak to the hollow site of the (111) microfacet at the step or the lower-terrace hollow site nearest to the step. By heating, site-to-site hopping to the more stable site occurs and the relative stability of four adsorption sites can be determined.