CuGaSe 2 (CGS) thin films grown on soda-lime and boro-silicate glass substrates by a chemical reaction of the precursor species, which were sequentially evaporated in a two stage process, were studied through spectral transmittance and x-ray diffraction (XRD) measurements, in order to investigate the effect of the substrate temperature and the selenium flow on the optical constants (refractive index n, absorption coefficient a and optical gap Eg) and on the structural properties (phase, crystalline structure and lattice parameters). Using the experimental measurements and computational tools that allow us simulating theoretically the transmittance and XRD spectra, the optical constants and the crystallographic parameters of the CGS films were calculated. These results showed that the mentioned synthesis parameters significantly affect the optical constants as well as the crystallographic properties of the CGS films.