The structural modification of tellurite optical glasses induced by rare-earth incorporation remains an important issue for optimizing their photonic functionality. In this work, TeO₂–ZnO–Yb₂O₃–Gd₂O₃ tellurite glasses were synthesized by the conventional melt-quenching method at ~800 °C in order to investigate the effect of Yb³⁺ and Gd³⁺ co-doping on the tellurite based network structure. The amorphous nature and structural evolution of the glasses were analyzed using Raman and Fourier-transform infrared (FT-IR) spectroscopy, which served as complementary methods for identifying the vibrational units of the glass matrix. Spectroscopic analysis reveals significant modifications in the distribution of TeO₄ trigonal bipyramids and TeO3/TeO3+1 structural units, accompanied by the formation of non-bridging oxygen (NBO) sites with increasing rare-earth ion (REI) incorporation. These changes indicate a gradual depolymerization and rearrangement of the tellurite network caused by the incorporation of Yb³⁺ and Gd³⁺ ions. The results demonstrate that the combined presence of these rare-earth ions significantly alters the local structural organization of the TeO₂–ZnO glass matrix. This study provides new insight into the structural role of Yb³⁺–Gd³⁺ co-doping in tellurite glasses, clarifying the relationship between rare-earth incorporation and the evolution of tellurite structural units. The findings contribute to the understanding of rare-earth-modified tellurite systems and their potential for near-infrared (NIR) photonic and multifunctional optical applications.