The experimental studies on phase equilibria in the quaternary system Na+,K+//Cl-,B4O72--H2O at 323 K were done by the method of isothermal solution saturation. Solubilities of salts and densities of the solution were determined experimentally. The experimental results show that there is no double salt in the quaternary system Na+,K+//Cl-,B4O72--H2O at 323 K. The equilibrium phase diagram and the density-composition diagram were plotted based on the experimental data. In the phase diagram, the quaternary system has two invariant points, five univariant curves, and four crystallization fields corresponding to Na2B4O7 center dot 10H(2)O, K2B4O7 center dot 4H(2)O, NaCl, and KCl. A brief discussion of the experimental results is described.