The Ge0.15Se0.85 alloy has been prepared in evacuated quartz tubes. Thin amorphous film of Ge0.15Se0.85 system has been prepared by using thermal evaporation technique with 400 +/- 5 nm thickness. Atomic absorption spectroscopy (AAS) was used to determine the concentration of the composite elements (Ge and Se). Amorphous structure was observed for prepared films by using X-ray diffraction (XRD). The optical properties of Ge0.15Se0.85 system have been studied as a function of annealing temperatures (T-a=300, 350, 400 and 450 K). The results showed that optical transitions are direct and indirect. The energy gap E-g increased with increasing annealing temperature, i.e the absorption edge shifts to lower wavelength. The refractive index, extinction coefficient and real and imaginary parts of dielectric constant for these films vary with heat treatment. Outcome of our study confirms that this system may be used for photovoltaic devices. (c) 2008 Elsevier Ltd. All rights reserved.