The solubility and the density in the aqueous ternary system (Li2SO4 + MgSO4 + H2O) at T = 308.15 K were determined by the isothermal evaporation. Our experimental results permitted the construction of the phase diagram and the plot of density against composition. It was found that there is one eutectic point for (Li2SO4 center dot H2O + MgSO4 center dot 7H(2)O), two univariant curves, and two crystallization regions corresponding to lithium sulphate monohydrate (Li2SO4 center dot H2O) and epsomite (MgSO4 center dot 7H(2)O). The system belongs to a simple co-saturated type, and neither double salts nor solid solution was found. Based on the Pitzer ion-interaction model and its extended H W models of aqueous electrolyte solution, the solubility of the ternary system at T = 308.15 K has been calculated. The predicted solubility agrees well with the experimental values. (C) 2008 Elsevier Ltd. All rights reserved.