Equilibrium phase relations and the solubility data for the rare earth trichloride RECl3 center dot nH(2)O (RE = La, n = 7; RE = Nd, Sm, Eu, n = 6) and cadmium chloride CdCl2 center dot 2.5H(2)O in the aqueous system were investigated. The corresponding equilibrium phase diagrams in the ternary system CdCl2-RECl3-H2O at 303 K were constructed. The results showed that these systems were complicated and consisted of four stable equilibrium solid phases [CdCl2 center dot H2O, CdCl2 center dot 2.5H(2)O, Cd4RECl11 center dot nH(2)O (n = 12, 14, 4:1 type), RECl3 center dot 7H(2)O] and a metastable phase [Cd8RECl19 center dot 16H(2)O (8:1 type)]. The new compounds Cd4RECl11 center dot nH(2)O and Cd8RECl19 center dot 16H(2)O were found to be incongruently soluble in the systems. The 4:1 type compounds obtained were identified and characterized by the method of X-ray diffraction, thermogravimetry, and differential thermogravimetry (TG, DTG).