The Effect of Sn addition in the structural and optical properties of Se–Te chalcogenide alloy at the expense of the Se content has been studied. Stoichiometric bulk ingot materials of the Se90−xTe10Snx (x=0, 2.5, 5 and 7.5 at%) were prepared by a melt-quench technique. X-ray diffraction (XRD) studies indicated that the investigated alloys confirmed its amorphous nature. These results were confirmed by scanning electron microscopy (SEM) investigations and correlated to the rigidity percolation threshold of the lattice. Stoichiometric thermally evaporated thin film of the obtained compositions were carefully characterized to establish the interdependence between their chemical composition and some physical parameters, such as the average heat of atomization (Hs), the cohesive energy CE, the average coordination number 〈Z〉 and the optical band gap (Eg). It has been found that all the parameters varied linearly when Sn content was increased. The variation in the optical band gap (Eg) with Sn addition was discussed in terms of the width of localized states (Ee) and a chemical bond approach model (CBA).