The equilibrium solubility of the quaternary system CdCl2-PrCl3-HCl (8.3 mass%)-H2O and the ternary system CdCl2-PrCl3-H2O at 298 K was investigated, and the corresponding phase diagrams were plotted. The results showed that the quaternary system was a complicated one consisting of four stable equilibrium solid phases CdCl2 (.) H2O, Cd8PrCl19 (.) 20H(2)O (8: 1 type), Cd4PrCl11 (.) 12H(2)O (4: 1 type), and PrCl3 (.) 7H(2)O, of which two new compounds Cd8PrCl19, 20H(2)O and Cd4PrCl11, 12H(2)O were found to be congruently soluble in the system. The ternary system consisted of four stable equilibrium solid phases (CdCl2 (.) 2.5H(2)O, CdCl2 (.) H2O, Cd4PrCl11 (.) 12H(2)O, and PrCl3 (.) 7H(2)O) and a metastable phase (Cd8PrCl19 (.) 20H(2)O). Two new compounds of the 8: 1 type and 4: 1 type were found to be incongruently soluble in the system. Both of the 8: 1 type and 4: 1 type compounds obtained were identified and characterized by the method of X-ray diffraction and the thermal analysis methods of thermogravimetry-differential thermogravimetry (TG-DTG).