The optical properties of polycrystalline silicides layers have been investigated by reflectivity measurements from the near I.R. to the near U.V. The influence of the metal nature (Ni, Pd, Pt) and of the silicide stoichiometry has been studied. The electronic den-sities of states have also been measured by X-ray photoemission spectroscopy. We show that two different classes of silicides may be distinguished independently of the metal. Metal rich silicides have optical spectra qualitatively similar to those of the metals. On the contrary, the reflectivity of Si rich silicides is very different. There appears a sharp near I.R. cut-off and well defined structures in the visible range. Based on published band structure calculations and our XPS measurements, we associate these phenomena to a partial decoupling between the free electrons contribution and the interband transitions from d derived states to the Fermi level.