The Tl2S-Sb2S3-Bi2S3 quasi-ternary system (system A) was studied using DTA, X- ray powder diffraction, microstructure examination, and microhardness measurements. TlSbS2-Tl4Bi2S5(TlBiS2, Bi2S3), Sb2S3-TlBiS2, Tl3SbS3-TlBiS2(Bi2S3), and [TlSb0.5Bi0.5S2]-Tl2S isopleths; isothermal sections at 500 K; and liquidus surface projection of system A were constructed. Characteristic features of the title system are extensive fields of solid solutions extended along the TlSbS2-TlBiS2 quasi-binary section and a continuous solubility belt 1-2 mol % wide extended along the Sb2S3-Bi2S3 binary subsystem. Primary separation fields of phases and the types and coordinates of invariant and monovariant equilibria in system A were determined.