The solubility isotherms of the ternary systems LiCl-MgCl2-H2O and Li2SO4-MgSO4-H2O were elaborately redetermined at 348.15 K using an isothermal equilibrium method. The compositions of solid phases were confirmed using the Scherinemakers' wet residue method. The ternary system LiCl-MgCl2-H2O is of a complex type with double salt LiCl center dot MgCl2 center dot 7H(2)O((s)) formed at 348.15 K, it gives the data of two invariant points for the first time and points out the boundary of three univariant curves and three crystallization fields corresponding to LiCl center dot H2O(s), MgCl2 center dot 6H(2)O((s)), and LiCl center dot MgCl2 center dot 7H(2)O((s)) clearly, which is more complete and accurate than the results in the literature at 348.15 K. In the ternary system Li2SO4-MgSO4-H2O, there are three solubility branches corresponding to the solid phases MgSO4 center dot nH(2)O((s)) (n = 6 and 1) and Li2SO4 center dot H2O(s); the phase field of MgSO4 center dot H2O(s) overlaps with the phase field of MgSO4 center dot 6H(2)O((s)), this finding indicates that the phase MgSO4 center dot H2O(s) is stable and MgSO4 center dot 6H(2)O((s)) is metastable; moreover, it gives the true equilibrium solubility data for MgSO4 center dot H2O(s) in the binary system MgSO4-H2O and the ternary system Li2SO4-MgSO4-H2O at 348.15 K and an invariant point which can point out the boundary of the two phase fields of MgSO4 center dot H2O(s) and Li2SO4 center dot H2O(s) definitely.