Amorphous thin films of Se100 − XSbX (X = 1, 5, 10, 15 and 20) were synthesized by flash evaporation of the premelt quenched bulk samples. The optical properties were investigated from spectrophotometric measurements in the UV-VIS-NIR spectral region using Swanepoel’s standard envelope method and related techniques. The optical band gap energy (Egopt) was evaluated from the Wemple-Didomenico (WDD) single oscillator model and Tauc’s extrapolation method in the region where the absorption coefficient, α ≥ 104 cm–1. The observed values of Egopt and oscillator energy Eo were found to decrease monotonously with increasing Sb additive. The complex dielectric constant (ε), Urbach energy (Eu), optical conductivity (σ), plasma frequency (ωp) and lattice dielectric constant (εL) were deduced for each alloy composition. The complex refractive index (n) fitted well to Sellmeier function which can allow extrapolation of n outside the measured spectral range. The observed changes in optical parameters with Sb content were explained on the basis of increased defect states and changes in cohesive energy indicators (average heat of atomization (Hs), mean coordination number 〈Z〉 and average single bond energy (Hs/〈Z〉).