Chalcogenide glasses with composition Ge20Se80−x Tl x (x=10, 15, 20, 25, 35%) have been prepared by the usual melt-quenching technique. Thin films of the mentioned compositions have been prepared by the electron beam evaporation. In addition, another set taken from the composition ofX=30 at % with different thicknesses (d=14.7, 30.0, 56.5, 70.0, 101.0, 180.0 nm) have been taken into consideration. The X-ray diffraction (XRD) analysis revealed the amorphous nature of the prepared films. It was found that, in contrast to the optical gap (E op), both the extent of the band tailing (B), and the band gap (E e) increase with increasing thallium content. In other side,E op showed thickness independency. The refractive index (n) showed obvious dependence on both composition and thickness also on the energy of the incident radiation.