Abstract: An experimental study on phase equilibria at 323 K in the ternary system KCl-K₂B₄O₇-H₂O was made by isothermal method.Phase equilibrium solubilities and densities of the solution were determined.Experimental results showed that the ternary system was a type of simple common saturation without double salt and solid solution.On the basis of solubility data， the phase diagram was plotted，which consisted of one invariant point，two univariant curves，and two crystallization zones，i.e. KCl-and K₂B₄O₇·4H₂O-crystallization zones.The equilibrium solid phase was KCl and K₂B₄O₇·4H₂O.The phase diagram showed that KCl had the salting-out effect on K₂B₄O₇. 

Key words: salt-water system, phase equilibrium, potassium salt