Phase equilibria of quaternary LiCl-NaCl-MgCl2-H2O and NaCl-Na2B4O7-MgCl2-MgB4O7-H2O systems at 273 K were studied by isothermal dissolution. The isothermal solubility of each salt was measured. Based on the experimental data and the corresponding equilibrium solid phases, equilibrium phase diagrams and water content diagrams were drawn. The results show that the quaternary LiCl-NaCl-MgCl2-H2O system forms a double salt LiCl center dot MgCl2 center dot 7H(2)O at 273 K. The phase diagram contains two invariant points, five univariant curves and four crystalline regions. The crystalline regions are LiCl center dot 2H(2)O, NaCl, MgCl2 center dot 6H(2)O and LiCl center dot MgCl2 center dot 7H(2)O, respectively. There are two invariant points, five univariant curves and four crystallizing fields in the quaternary NaCl-Na2B4O7-MgCl2-MgB4O7-H2O system at 273 K, and the corresponding crystallizing fields are NaCl, Na2B4O7 center dot 10H(2)O, MgCl2.6H(2)O and MgB4O7 center dot 9H(2)O.