Mineral solubilities in the ternary system MgCl2 + SrCl2 + H2O and the quaternary system NaCl + MgCl2 + SrCl2 + H2O at 288 K were measured using the isothermal dissolution equilibrium method. Two phase diagrams were drawn and both of them were of simple cosaturation type. The ternary system MgCl2 + SrCl2 + H2O contains one invariant point, two isothermal solubility curves, and two crystallization fields (MgCl2 center dot 6H(2)O and SrCl2 center dot 6H(2)O). The quaternary system NaCl + MgCl2 + SrCl2 + H2O consists of one invariant point, three isothermal solubility curves, and three crystallization fields (NaCl, MgCl2 center dot 6H(2)O, and SrCl2 center dot 6H(2)O). At the same time, the comparisons of the ternary system MgCl2 + SrCl2 + H2O at different temperatures were conducted. The results show that the solubility of magnesium chloride changes greatly with the increase of the temperature, which can guide the separation of magnesium chloride and strontium chloride in brines.