Solid-liquid equilibria in the ternary system (CsCl + DyCl3 + H2O) and the quaternary system {(CsCl + DyCl3 + HCl (similar to 10.7%) + H2O} at T= 298.15 K and under 101.3 kPa were investigated by the method of isothermal solution saturation, and the corresponding phase diagrams were constructed. It was found that there were three crystallization regions corresponding to CsCl, Cs2DyCl5 center dot 6H(2)O and DyCl3 center dot 6H(2)O in the ternary system. Nevertheless, four crystallization regions corresponding to CsCl, Cs5DyCl8 center dot 6H(2)O, Cs2DyCl5 center dot 6H(2)O and DyCl3 center dot 6H(2)O were found in the quaternary system. The compound Cs2DyCl5 center dot 6H(2)O was congruently soluble in the two systems, and new double salt Cs5DyCl8 center dot 6H(2)O was formed in the quaternary system which was congruently soluble in an average medium of similar to 10.7 mass% HCl. The new solid-phase compounds Cs5DyCl8 center dot 6H(2)O and Cs2DyCl5 center dot 6H(2)O were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs5DyCl8 center dot 6H(2)O and Cs2DyCl5 center dot 6H(2)O in water were measured to be (44.28 +/- 0.50) kJ.mol(-1) and (5.32 +/- 0.27)kJ.mol(-1) by microcalorimetry in the condition of infinite dilution, and their standard molar enthalpies of formation were determined to be -(5086.9 +/- 1.3)kJ.mol(-1) and -(3771.6 +/- 0.9)kJ.mol(-1). As part of this work, five compounds Cs3LaCl6 center dot 3H(2)O, CsLaCl4 center dot 4H(2)O, CsCeCl4 center dot 4H(2)O, CsPrCl4 center dot 6H(2)O and CsNdCl4 center dot 9H(2)O were synthesized according to the literature [18-21]. The molar enthalpies of solution of Cs3LaCl6 center dot 3H(2)O, CsLaCl4 center dot 4H(2)O, CsCeCl4 center dot 4H(2)O, CsPrCl4 center dot 6H(2)O and CsNdCl4 center dot 9H(2)O in water were also measured to be (14.78 +/- 0.31) kJ.mol(-1), -(30.98 +/- 0.62) kJ.mol(-1), -(20.26 +/- 0.22) kJ.mol(-1), -(19.64 +/- 0.54) kJ.mol(-1)and -(5.86 +/- 0.45) kJ.mol(-1 )in the condition of infinite dilution, and their standard molar enthalpies of formation were calculated to be -(3351.1 +/- 1.1) kJ.mol(-1), -(2740.3 +/- 1.0) kJ.mol(-1), -(2746.1 +/- 0.7)kJ.mol(-1), -(3326.8 +/- 0.9) kJ.mol(-1) and -(4189.7 +/- 0.9) kJ.mol(-1), respectively. (C) 2019 Elsevier Ltd.