The Sb₂S₃–InSb₂Se₃S system has studied using the method ofdifferential-thermal analysis, X-ray diffraction, microstructural analysis and microhardness and density measurements. It is established that the latter is partially nonquasi-binary section of quaternary system Sb,In||S,Se and has complex character. At the room temperature in the  system Sb₂S₃ base solid solutions in reach 3 mol.% InSb₂Se₃S, and InSb₂Se₃S based solid solution extends to
7 mol.% on Sb₂S₃