The solubilities of salts in the (NaBr + MgBr2 + CaBr2 + H2O) system and its two ternary subsystems (NaBr + MgBr2 + H2O) and (NaBr + CaBr2 + H2O) are investigated at 298.15 K by the isothermal dissolution equilibrium method. The equilibrium phase diagrams of the three systems were obtained using the experimental results. In the three systems, neither solid solution nor double salt was found. In the two ternary phase diagrams, there are two invariant points, three dissolution equilibrium curves and three crystallization fields. The equilibrium solid phases in the (NaBr + MgBr2 + H2O) system are NaBr, NaBr center dot 2H(2)O and MgBr2 center dot 6H(2)O, and those in the (NaBr + CaBr2 + H2O) system are NaBr, NaBr center dot 2H(2)O and CaBr2 center dot 6H(2)O. The phase diagram of the quaternary system at 298.15 K consists of one invariant point, four solubility curves and four regions (corresponding to NaBr, NaBr-2H(2)O, MgBr2 center dot 6H(2)O, and CaBr2 center dot 6H(2)O). The solubilities of salts in the quaternary system and its two subsystems were calculated at 298.15 K by Pizter equation. The predicted results are in agreement with the experimental results.