The structural and optical properties were studied-of CuGaSe, polycrystalline thin films with thicknesses in the range 2000-5600 angstrom deposited by thermal evaporation. Analysis of the absorption coefficient data revealed the existence of several energy bands at 1.64. 1.73, 1.93 and 2.1 eV in the photon energy range 1-3 eV. The effect of thickness and thermal treatment on the values of energy gaps is discussed in terms of the structure of the films. The dependence on frequency of the optical constants n, k, epsilon’, and epsilon" was also determined. The high frequency dielectric constants epsilon’ and epsilon", as estimated from extrapolation of the curves to the high frequency range, are 12 and 1.52 respectively.