Phase equilibriums in the AgTl₃J₅–TlJ–J system were investigated using DTA and X-ray analysis. Polythermal sections AgTl₃J₅–Tl₃J₄  and AgTl₃J₅–TlJ₃, as well as liquidus surface projection were constructed. Fields of primary crystallization of phases were determined, and types and coordinates of non- and monovariant equilibriums were established. It was shown, that AgTl₃J₅–Tl₃J₄  and AgTl₃J₅–TlJ₃ sections are stable below solidus and divide system on to 3 three-phase area