The isothermal dissolution equilibrium method was used to determine the solubilities of salts and the equilibrium solid phases in the two ternary systems: Li2SO4 Li2B4O7 H2O and K2B4O7-K2SO4-H2O at 273 K. These results are also used to construct phase diagrams of the two ternary systems. Both phase diagrams have an eutectic point, two univariant solubility curves, and two crystallization regions of single solid phase. At the eutectic point of the ternary system Li2SO4 Li2B4O7 H2O, the coexisting solid phases are Li2B4O7 center dot 3H(2)O and Li2SO4 center dot H2O; at the eutectic point of the ternary system K2B4O7-K2SO4-H2O the coexisting solid phases are K2BO7 center dot 4H(2)O and K2SO4.