Abstract: Two surfaces correponding to LaCl_3 and α-solid solution(MgCl_2.LiCl) respectively: and one secondary crystallization curve with a minimum M at 63.8 wt-% LaCl_3,2.0 wt-% MgCl_2,34.2 wt-% LiCl and 492℃ were fonud by means of DTA.In combination with liquidus determination.an approach was also made to the alteration in LnCl_3-MgCl_2-LiCl svstem,where Lu denotes La.Ce.Pr or Nd.

Key words: LaCl_3-MgCl_2-LiCl, LaCl_3, system phase diagram