By methods of differential-thermal roentgenphase and microstructural analyses CuSbS₂–LaSbS₃ and CuSbS₂–NdSbS_3­ systems have been investigated first and their state diagrams have been plotted. It is established that in the systems congruently melting compounds of Cu₂LnSb₃S₇ composition are generated. On the base of roentgenstructural  analysis it is established that the compounds Cu₂LaSb₃S₇ – a=14.43, b=21.42, c=3.97Å; Cu₂NdSb₃S₇ – a=14.463, b=21.404, c=3.962 Å crystallize in the rhombic syngony