Chalcogenides are promising material for various optical applications. Transmission spectra of thermally evaporated thin film of Ge19Se81 Sb-x(x) (where x = 0, 4, 8, 12, 16, 17.2, 20) have been obtained in the spectral range of 400-2400 nm. Refractive index has been found to increase with increase in Sb content while optical band gap has been found to decrease up to x - 17.2 and thereafter increases. The results have been explained on the basis of change in the density of dangling bonds. Results indicate that the observed characteristics favour the application of these materials in optical filters. (C) 2012 Elsevier B.V. All rights reserved.