The metastable phase equilibrium of the quinary aqueous system Li+ + K+ + Cl- + CO32- + B4O72- + H2O was investigated at 273.15 K using an isothermal evaporation method. The solubilities and densities of the equilibrated solution were determined. Based on the experimental data, the space metastable phase diagram and the projected phase diagram saturated with salt Li2CO3 of the quinary system at 273.15 K were constructed. The projected phase diagram of this system consists of three invariant points, seven univariant curves, and five crystallization fields corresponding to the single salts LiCl. H2O, KCl, K2B4O7.4H(2)O, K2CO3.3/2H(2)O, and LiBO2.8H(2)O. Comparisons between the phase diagrams at 273.15 K and at 298.15 K show that the crystallization form of lithium borate is LiBO2.8H(2)O at 273.15 K, which formed as Li2B4O7.5H(2)O at 298.15 K.