Abstract: The solubilities and the refraction indices of the saturated solutions in the titled system have been investigated isothermally. The system at 30℃ and at 50℃ is a simple eutonic one. The solubilities of LaCl₃ · 7H₂O (one of the solid phases) and CH₃CONHCSNH₂ (the other solid phase) at 30℃and at 50℃ decrease from 49.32%, 2.20% and 51.68%, 4.71% in pure water to 49.21%, 0.44% and 51.58%, 0.62% in eutonic solutions ( by LaCl₃ and CH₃CONHCSNH₂), respectively.