Glasses of chemical formula xEr2O3. (55-x) ZnO. 45SiO2 (x = 0, 0.5, 1, 3, 5, 7, 10, and 15 mol. %) were prepared using the melt-quenching route. The structure of the glasses was investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, and NMR spectroscopy. XRD data confirmed that all zinc silicate glasses containing Er2O3 had an amorphous glassy structure. XRD showed the presence of two humps around 50° and 60° that are related to Er and Zn ions incorporated into the glass structure, and these humps' intensity changed with Er2O3 addition. The fraction of different silicate structural units is studied using FTIR and Raman spectroscopy, which is comparable to that obtained from the reported NMR values. FTIR, Raman, and NMR measurements confirmed the dual role of Er2O3 on the structure of zinc silicate glasses. Based on these results, Er2O3 content is below 5 mol. % entered as a glass modifier, creating more non-bridging oxygen atoms (NBO, increases Q1) while above 5 mol. % played a glass former, creating more bridging oxygen atoms (BO, increases Q2). Thermal heat treatment was applied for all glass samples according to DSC measurements. The thermal parameters have been discussed and correlated with the glass structure. The glass transition temperature (Tg) escalated from 377.3 at 5 mol. % to 391.04 °C at 15 mol. % Er2O3. The crystallization temperature (Tc) also increased from 548.27 °C to 598.37 °C, and the Vickers hardness (Hv) improved markedly from 646.4 kg/mm2 at 0 mol. % to 732.2 kg/mm2 at 15 mol. % Er2O3. XRD and FTIR results for glass samples after heat treatment for 24 h at 700 °C have been discussed regarding the crystallization of the glass matrix. These findings highlight the critical role of Er2O3 in modifying glass structure and properties, demonstrating its potential to enhance the glass matrix's durability and mechanical strength.