Phase equilibriums in the Tl5Te3-Tl4PbTe3-Tl9NdTe6 system have been investigated using DTA, EMF, 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, EMF and parameters of crystal cage on concentration constructed. It was established that the system is characterized by formation of non-limited solid solutions with tetragonal structure as Tl5Te3 type.