Thin films of Ge 28− x Se 72 Sb x (x=0, 8, 16, 24at%) with thickness of 200nm are prepared by thermal evaporation onto glass substrates under vacuum of 5.3×10 −5 mbar. Optical reflectance and transmittance of these films are measured at room temperature in the light wavelength region from 200 to 1100nm. The estimated optical energy gap, E g , is found to decrease from 2eV (0at% Sb) to 1.5eV (24at% Sb), whereas the band tail width, E e , increases from 0.062 to 0.077eV, respectively. The refractive index, n, and extinction coefficient, κ, are determined as functions of wavelength. The DC electrical conductivity, σ, of films is measured as a function of temperature in the range from 300 to 360K. The extracted value of activation energy, ΔE, is found to decrease from 0.95eV (0at% Sb) to 0.74eV (24at% Sb). Optical and electrical behavior of films can be explained in terms of cohesive energy (CE) and Se–Se defect bonds.