An isothermal evaporation method was employed to study the solubilities of the aqueous quaternary system Li+, Na+//CO32-, SO42--H2O at 273.15 K, and the corresponding densities of the equilibrated solution were determined by the specific gravity bottle method. According to the experimental data, the metastable phase diagram, the water content diagram, and the density versus composition diagram were constructed. Results indicate that the quaternary system is of a complex type due to the two double salts Na3Li(SO4)(2)center dot 6H(2)O and 2Na(2)SO(4)center dot Na2CO3 formed. There are four invariant points, six crystallization fields corresponding to four single salts (Li2CO3, Li2SO4 center dot H2O, Na2SO4 center dot 10H(2)O, and Na2CO3 center dot 10H(2)O) and two double salts (Na3Li(SO4)(2)center dot 6H(2)O and 2Na(2)SO(4)center dot Na2CO3) in this metastable phase diagram. The comparison was made between the metastable phase diagrams at 273.15 K and at 288.15 K and also between the metastable phase diagram at 273.15 K and stable phase diagrams at (298.15, 323.15, and 373.15) K. Results show that double salt 2Na(2)SO(4)center dot Na2CO3 is formed at T = (273.15, 323.15, and 373.15) K, while it is not formed at T = (288.15 and 298.15) K.