Within the Tl 2 O–Ag 2 O–TeO 2 system, a large glass-forming domain was evidenced and is presented for the fist time. Densities, glass transition (T g ) and crystallization (T c ) temperatures of the relevant glasses were measured. A structural approach of these glasses as functions of the composition was performed using Raman scattering. The Raman spectra were analysed in terms of the structural modifications induced by the Tl 2 O and Ag 2 O modifiers. It has clearly evidenced a phase separation inherent in tellurite glasses with low valence cations (as Tl + and Ag + ). The glasses would be constituted of two phases only: one of pure TeO 2 and one of pure ortho-tellurite M 2 TeO 3 (M=Ag, Tl) with the statistically mixed Ag–Tl cationic composition.