The method of isothermal dissolution equilibrium was used to study the solubilities of salts and the densities of saturated solutions in the two quaternary systems KCl-K2B4O7-K2SO4-H2O and MgCl2-MgB4O7-MgSO4- H2O at 273 K. The equilibrium solid phases were also determined by the method of X-ray diffraction. On the basis of experimental results, the phase diagrams and density versus composition diagrams of those quaternary systems at 273 K were plotted. The results indicate that both the phase diagrams of the two systems consist of one invariant point, three stable solubility isothermal curves, and three crystalline regions. The crystallization fields for the system KCl-K2B4O7-K2SO4-H2O correspond to K2B4O7 center dot 4H(2)O, KCI, and K2SO4. Those for the system MgCl2-MgB4O7-MgSO4-H2O correspond to MgB4O7 center dot 9H(2)O, MgCl2 center dot 6H(2)O and MgSO4 center dot 7H(2)O.