The solid-liquid equilibria in the ternary system CaBr2-MgBr2-H2O and quaternary system NaBr-KBr-SrBr2-H2O at 348 K were determined with the method of isothermal solution saturation. Also determined are the densities of saturated solutions. The phase diagram of the ternary system CaBr2-MgBr2-H2O has two invariant points, three univariant curves and three crystallization fields (which are saturated with MgBr2 center dot 6H(2)O, 2CaBr(2)center dot MgBr2 center dot 12H(2)O, and CaBr2 center dot 2H(2)O, respectively). The phase diagram of the quaternary system NaBr-KBr-SrBr2-H2O includes one invariant point, three univariant curves and three crystallization fields (which are saturated with SrBr2 center dot 6H(2)O, NaBr, and KBr, respectively). On the basis of the extended Harvie-Weare (HW) model and its temperature-dependent equation, the mixing ion interaction parameters theta(Mg,ca), Psi(Mg,ca,Br) and the dissolution equilibrium constant K for MgBr2 center dot 6H(2)O, CaBr2 center dot 2H(2)O, and 2CaBr(2)center dot MgBr2 center dot 12H(2)O in the ternary system at 348 K were fitted by using the Pitzer equations and the multiple linear regression method. A chemical model was constructed to calculate the solubility curves by using the Pitzer equations in the ternary systems MgBr2-CaBr2-H2O at 348 K The calculated solubilities are in agreement with experimental data.