Solid-liquid equilibria in the quaternary systems NaBr-KBr-MgBr-HO and KBr-NaBr-CaBr-HO at 348.15 K were determined using the method of isothermal solution saturation. The solubilities of the equilibrium solutions were determined. According to the experimental data, the equilibrium phase diagrams and water content diagrams of the two quaternary systems were plotted. The solubility diagram of the quaternary NaBr-KBr-MgBr-HO system has two invariant points, five univariant curves, and four crystallization fields (which are saturated with MgBr·6HO, KBr·MgBr·6HO, NaBr and KBr, respectively, where KBr·MgBr·6HO is a double salt). The solubility diagram of the quaternary system KBr-NaBr-CaBr-HO includes one invariant point, three univariant curves, and three crystallization fields (CaBr·2HO, KBr and NaBr). The dissolution equilibrium constant K of NaBr, KBr, MgBr·6HO, KBr·MgBr·6HO and CaBr·2HO at 348.15 K were fitted using Pitzer's equation. A chemical model based on the Pitzer equation was constructed to calculate the solubilities of salts in the two quaternary systems at 348.15 K. The calculated solubilities are in agreement with experimental results. [ABSTRACT FROM AUTHOR]