The molalities b of (b(1)LiBr + b(2)MgBr(2))(aq) have been investigated in saturated solutions at the temperature T = 348.15 K by the physicochemical-analysis method and crystallization of the crystalline hydrates LiBr . H2O and MgBr2 . 6H(2)O alone has been established. A thermodynamic approach based on the Fitter model has been used for plotting the theoretical solubility isotherm. The thermodynamic functions (osmotic coefficients, binary parameters of ionic interaction, thermodynamic solubility products) needed for simulation of the corresponding binary solutions have been calculated using empirical approximating equations which express the dependence of osmotic coefficients and binary parameters on temperature. The ternary Pitzer parameters are calculated using experimental solubilities of the saturated ternary solution. Good agreement between experimental and calculated solubilities has been found.