Lu/sub 2/O/sub 3/ thin-film coatings of a thickness 0.1-1.3 mu m were deposited onto quartz plates by an electron beam gun. Optical measurements were carried out for the wavelengths lambda =0.2 mu m-2.5 mu m. All fabricated coatings were highly transparent in the spectral range from 0.3 mu m to 2.5 mu m. Optical constants of Lu/sub 2/O/sub 3/ films have been determined from the spectrophotometrically measured transmittance. The dispersion n( lambda ) and extinction k( lambda ) curves in the spectral range considered have been presented and analysed. The refractive index for Lu/sub 2/O/sub 3/ films has been estimated as 1.84 at 0.55 mu m. The characteristics of the real and imaginary parts of the dielectric function epsilon *(v) are also presented. Values of epsilon '/sub infinity /=323-3.53 have been obtained as the high-frequency optical relative permittivity for Lu/sub 2/O/sub 3/ thin films.