Synthesis and characterization of quaternary erbium tellurite glass within the molar percentages of (75-x) TeO2-20ZnO-5Na(2)O-xEr(2)O(3) where (0 <= x <= 2.5) were carried out. The optical properties were determined by recording the UV-Vis spectra in the range 200-800 nm which exhibited increasing the band gap with increasing Er2O3. The thermal characteristics of the glass were determined and showed higher thermal stability of the system suggesting its applicability for fiber drawing. The heat treatment was performed for the samples (0.5 and 2.5 mol %) of Er2O3 at different temperatures and times. Zn-2 Te3O8, TeO2, ZnO, Er2TeO6, Er6Te5O19.2 and Er(2)O(3 )phases were identified, characterized and found to be in nanoscale. The annealing operation made the optical energy gap to decrease after the structure changes.