It is found that the SnO2 nanometer particle modified by chemical methods on its surface with a layer of steric acid molecules has a significant red shift of optical absorption band edge and clear photoluminescence at room temperature, which is in contrast with that of bulk SnO2 and naked SnO2 nanometer particles. It is concluded that these results are related to the dielectric confinement effects on the SnO2 nanometer particles surfaces.