Ga 80−x Se x Te 20 amorphous system was prepared by conventional technique. Structural, morphology and optical properties have been investigated. X-ray diffraction (XRD) patterns reveal the non-crystalline nature of the prepared sample. Differential thermal analysis (DTA) traces indicate the presence glass transition temperature T g for all samples below 500˚C. Addition T g values increases by increasing Se content. Energy dispersive X-ray spectroscopy (EDX) data shows good agreement with actual composition. Moreover, surface characterization was achieved by scanning electron microscope (SEM). The patterns confirmed the non-crystalline nature. In order to analyze the data, the cohesive energy C.E was calculated by all three composition optical properties that have been investigated in the wavelength range 500 -2500 nm. Reflectivity R and transmitivity T spectrum were used to estimate the band gap energy using UV-Visible absorption spectrum. It is worthy mention that the optical band gap follows the T g and cohesive energy behavior, where it increases by increasing Se content.