The optical properties of amorphous Ga20Se80−xBix(a-Ga20Se80−xBix) thin films (where x = 0, 5, 10, 15 and 20) have been studied in the wavelength range (450-1400 nm). It is found that the optical bandgap decreases with increasing bismuth content in the a-Ga20Se80−xBixsystem. The value of the refractive indexndecreases, while the value of the extinction coefficientkincreases with increasing photon energy. The dc conductivity measurements of a-Ga20Se80−xBixthin films have also been reported in the temperature range 287-318 K. It is observed that the activation energy decreases with increase in the metallic impurity in a-(Se-Ga) binary alloys.