The equilibrium solubility of the quaternary system HoCl3-CdCl2-HCl-H2O was determined at 298.15 K, and the corresponding equilibrium diagram was constructed. The quaternary system is complicated with three equilibrium solid phases, CdCl2 center dot H2O, Cd4HoCl11 center dot 14H(2)O (4:1 type), and HoCl3 center dot 6H(2)O, of which the new compound Cd4HoCl11 center dot 14H(2)O was found to be congruently soluble in the system. The new compound obtained was identified and characterized by the methods of X-ray diffraction, thermogravimetry, and differential thermogravimetry. The standard molar enthalpy of solution of Cd4HoCl11 center dot 14H(2)O in deionized water was measured to be (15.74 +/- 0.18) kJ.mol(-1) by heat conduction microcalorimetry. Its standard molar enthalpy of formation was calculated to be (-6864.7 +/- 1.3) kJ.mol(-1). The standard molar enthalpy of formation, the solubility data, and the phase diagram of the quaternary system could provide the fundamental basis and serve as a guide for the preparation of Cd4HoCl11 center dot 14H(2)O.