The PbBi₂S₄–PbNd₂S₄ system of Pb–Bi–Ln–S quaternary system was studied by using physico-chemical analysis methods and the formation of quaternary sulfide PbNdBiS₄ melting congruently  at 1145 K was determined. Compound PbNdBiS₄ is a phase of variable composition. For the first time the compunds of PbLnBiS₄ (Ln=La÷Er) type have been synthesized  and their standart thermodynamic functions have been calculated.