We have measured the optical properties of epitaxial CoSi2films on Si from 0.062 to 2.76 eV by ellipsometry and spectrophotometry. The energy dependencies of the dielectric constants show Drude behavior at energies lower than ∼0.2 eV with Drude parameters ℏ&ohgr;p=(5.8±0.2) eV and ℏ/&tgr;=(0.09±0.02) eV. Using the measured optical constants, the CoSi2film is shown to have maximum absorptance at a thickness of ∼20 nm for &lgr;≳1.4 &mgr;m. Finally, we have calculated the absorptance of a composite film of CoSi2particles embedded in Si and found that the absorptance peak due to a surface plasmon resonance in the CoSi2particles shifts to higher energy as the ellipsoidal particles become more elongated, in agreement with recent observations by Fathaueretal. [Phys. Rev. B44, 1345 (1991)].