sing methods of differential thermal and X-ray analyses the phase equilibriums in TlBiSe2-AgBiSe2-Bi2Se3 (A) system are investigated.Tl0,5Ag0,5Bise2-Bi2Se3 polythermal section, isothermal sections of phase diagram at 800 and 500 K, as well as the projection of liquidus surface are constructed. It was established that the system (A )is of three-phase eutectic type. The continuous solid solutions (δ-phase) in the section of TlBiSe2-AgBiSe2 formed in terms of high-temperature cubic modifications of initial selenides considerably penetrate into concentration of triangle (A) to occupy more than half of its area at 800 K. Decomposition of the δ-phase on two mutually-sated solid solutions (δ/ and δ//) begins at 700 K. This solid solutions by eutectic reaction at 540 and 555 К grow into in solid solutions on the basis of low-temperature modifications of TlbiSe2 (γ1) and AgBiSe2(γ2)compounds.