The solubilities in the thermodynamic phase equilibria of the LiBr-NaBr-KBr-H2O system and its two subsystems LiBr-NaBr-H2O and LiBr-KBr-H2O at 298.15 K were investigated experimentally by the isothermal solution equilibrium method. Relevant stable-phase diagrams were plotted based on the experimental results. Using Pitzer's solution model, nonreported mixing parameters Psi(Li,Na,Br) and Psi(Li,K,Br) were acquired and the solubilities of three systems were also predicted at 298.15 K. The results show that good agreement was obtained between calculated and experimental values.