The morphology and NO reactivity of Rh deposited on a thin Al2O3 film were studied by means of x-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and noncontact atomic force microscopy. The NO dissociation activity of the Rh deposited on the Al2O3 surface was higher than that of Rh(111). The NO dissociation kinetics and the NO and CO adsorption properties of the Rh/Al2O3 surface indicated that the surface structure of the supported Rh mainly consisted of a (100) face. The supported Rh existed as small particles on the step sites of the Al2O3 surface. Thus, the authors believe that the low-coordinated step sites of Al2O3 played a role in formation of the (100) surface structure.