Phase equilibriums in the Tl₅Te₃–Tl₄PbTe₃–Tl₉NdTe₆ system were investigated using DTA, e.m.f. of concentration circuits, X-ray methods and measurement of microhardness. Projection of liquidus and solidus surfaces, some isothermal and polithermal sections of phase diagram and graphics of dependence of microhardness, e.m.f. and parameters of crystal cage on concentration were constructed. It was established, that the system is characterized by formation of non-limited solid solutions with tetragonal structure of Tl₅Te₃ type