Abstract: Both the isotherms of solubilities and refraction indices of the system consist of three branches corresponding to the solid phases: LaCl₃·7H₂O, LaCl₃·2CH₃ CONHCONH₂·5H₂O and CH₃CONHCONH₂. Two eutonics contain LaCl₃ and CH₃CONHCONH₃ 47.68%, 8.48% and 41.63%, 15.64%, respectively. The ternary compound is an incongru-ently soluble one. Its density determined as described in the previous work is adout 1.75(17℃). Its photomicrograph is also given in this paper.