By re-examining SnS-PbS system by physical-chemical analysis methods specific results were obtained. It was determined that at 1:1 correlation of the system, PbSnS2 containing compound is obtained. This compound is crystallized at rhombic syngony with parameters: a=4.30, b=4.04, c=11.22 Å. PbSnS2 compound is isostrustural to SnS compound, at the same time there is double-sided solid solution area around PbSnS2. On the basis of SnS – 10 mol% PbS and on the basis of PbS – 15 mol% SnS dissolution area has been identified and state diagram of system was plotted.