The TI-Ga-S ternary systerii was studied systematically and four new phases or mixed crystal series were synthesized at 300℃.TI4GaS5, as a new ternary phase,occurs along the TIS-Gas join. The Tl-rich solid solution series- phass I exists on the Tl4S3-GaS join with composition from T120GaS16(A) to T120Ga2S17(B).The mixed crystal series phases II and III were identified in the central portion of the diagram. Phase II s.s. extends on the T1S-Ga2S3 join with compositors ranging from TIsGasSOF)-TIZGaSs(E) up to T11oGasS}, (D).The composition region of Phase IIIs.s. extends from T1GaS2(H) on the T12S-Ga2S3 through T18Ga6S15(K) on the Tl4S3-Ga2S3 join up to T12Ga2S5 on the T1S-Ga2S3 join. The phase relations at 300℃ are shown. it the figure. In addition, a mixed crystal series was confirmed at 630-900℃，and its composition extends from TI2Ga10S11( J) on the TI2S-GaS join to TIGa5S8( I)on the T12S-Ga2S3 join. The X-ray powder diffraction lines were indexed.