Abstract Physicochemical studies of interaction and glass formation in the As2Te3-Tl2Se system were carried out using the following methods: differential thermal analysis (DTA), X-ray diffraction analysis (XRD), microstructural analysis (MSA), and by measuring microhardness and density, T-x was constructed phase diagram. The system is a partially quasi-binary diagonal section of the ternary reciprocal system Tl,As//Se,Te. When the component ratio is 1:1, a quaternary compound of the composition Tl2As2SeTe3 is formed, which melts congruently at 270°C. It has been established that the Tl2As2SeTe3 compound crystallizes in the tetragonal syngony with lattice parameters: a=11.47 Å; c=9.50 Å, z=6, ρpucn. =7.98 g/cm3, ρX-ray =8.13 g/cm3. In the system at room temperature, solid solutions based on As2Te3 reach 3.3 mol % Tl2Se, and solid solutions based on Tl2Se are practically not established. Under normal conditions, extensive areas of glass formation based on Tl2As2SeTe3 were found in the concentration range of 35-70 mol % Tl2Se.