Abstract: The phase relationship and physicochemical properties，such as densities，refractive indices，and pH，of the equilibrated solution in the ternary system Li⁺，K⁺ //borate-H₂O were investigated at 348 K by using isothermal solution equilibrium method.On the basis of experimental data，the stable phase diagram and the physicochemical properties vs.composition diagram of the ternary system at 348 K were constructed.Results showed that the ternary system was a type of simple common saturation，no double salt or solid solution formed.In the stable phase diagram，there were one invariant point，two univariant curves，and two crystallization fields corresponding to single salts Li₂B₄O₇·3H₂O and K₂B₄O₇·4H₂O，respectively.K₂B₄O₇ had solubilization effect on Li₂B₄O₇.The physicochemical properties changed regularly with the variation of the mass fraction of K₂B₄O₇，they increased with the increase of the mass fraction of K₂B₄O₇ on the univariant curve AE，while decreased with the increase of it on the univariant curve BE，and reached the maximum value at the invariant point E.

Key words: ternary system, phase equilibrium, lithium, borate, potassium