Abstract: The titled ternary compound has been prepared by mixing LaCI₃·7H₂O and CH₃CONH₂ in water with l：4 of the mole ratio of LaC1₃ to CH₃CONH₂。The solublities in the titled system at various temperatures as wellas the melting point of the ternary comPound were determined． Accor－ding to thesedata adlagram ofsolublllty ofblnary system LaCI₃·4CH₃CONH₂·5H₂0－H₂O was plotted．The temperature of the eutecticpoint is at－34．5℃ containing the ternary compound 61．3％． Theternary compound Is congruentlysoluble In water covering the tempera－ture range from the eutectlc point to its melting point．