Metastable equilibrium solubilities and densities of quaternary system Li2SO4＋Li2CO3＋ Li2B4O7＋H2O at 288 K were determined by isothermal evaporation method. According to the experimental data, the metastable equilibrium phase diagram was plotted. The metastable phase diagram had one invariant point F, three double saturated liquid curves ElF, E2F and E3F, and three crystallization fields corresponding to Li2SO4·H2O, Li2CO3 and LiBO2·8H2O. It was found that lithium sulphate（Li2SO4） had the highest concentration and strong salting-out effects on the other salts. There were no solid solutions or double salts formed in the quaternary system at 288 K.
Metastable equilibrium solubilities and densities of the Li2SO4 ＋ K2SO4 ＋ Li2CO3 ＋ K2CO3 ＋ H2O system at 288 K were determined experimentally by using the isothermal evaporation method. According to the experimental data, the metastable equilibrium solubility phase diagram was constructed. In the phase diagram, there are three invariant points, seven univariant curves, and five fields of crystallization： Li2SO4· H2O2,K2SO4, Li2CO3, K2CO3 · 3/ 2H2O and K2SO4· Li2SO4. The double salt K2SO4 · Li2SO4 was found in the metastable equilibria. Lithium carbonate（ Li2CO3 ） has the smallest solubility in the quaternary system.
