Amorphous Sb₁₀Se₉₀ thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500–900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple–Didomenico single oscillator model. The oscillator energy E₀ and the dispersion energy E_d have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.