Optical parameters of Cu(In,Ga)Se-2 (CIGS) thin films were determined by measuring optical transmission and reflectance spectra at room temperature. CIGS thin films with average Ga/(Ga + In) ratio 0.45 were deposited on glass substrates using a three-stage process. The films had thickness d 1.6 mu m and refractive index n 2.38-2.53 in the transparency range. The band-gap energy E-g of the CIGS thin films was 1.36 eV at 293 K. The influence of chemical composition heterogeneity along the depth of the absorbing layers on the spectral position of the fundamental absorption edge of the CIGS solid solutions was discussed.