To study the influence on the optical properties of metal imposed by neighboring medium,we used Dove prisms with different refractive indexes as the substrate in experiment.The noble metal films of Au and Ag were deposited on the bottom of prisms.The dielectric functions for films at the metal-air and metal-substrate interfaces were measured by the spectroscopic ellipsometric method.We found that the dielectric functions of the film measured at the metal-substrate interface do change with the refractive index of the neighboring medium and differ from that measured at the metal-air interface in both the Drude and interband transition regions.The results obtained in a solid-contacting configuration agree with those observed by other authors in a liquid-contact condition,however they cannot be well understood by the known mechanisms.