Abstract: Phase equilibrium of quaternary saline system NaOH-Na₂SnO₃-Na₂PbO₂-H₂O, ternary saline system NaOH-Na₂SnO₃-H₂O and NaOH-Na₂PbO₂-H₂O were determined by employing the method of isothermal solution saturation at 20 ℃, 40 ℃ and 60 ℃. The results show that solubility of Na₂SnO₃ in ternary system decreased with increasing of alkalinity, and solubility at 40 ℃ was higher in solution with high alkalinity. Solubility of Na₂PbO₂ in ternary system increased with the increasing of the temperature, but its change with alkalinity followed an S-shape curve. In the quaternary system, interaction between Na₂SnO₃ and Na₂PbO₂ was observed, however, their solubility had the same trend with that in ternary systems. Conclusions obtained in this study can be used as basic data for separation of NaOH, Na₂SnO₃ and Na₂PbO₂.