Liquid-liquid equilibrium. data have been measured for one ternary system of water + N-methyl-2-pyrrolidone + 1-hexanol and three quaternary systems of water + N-methyl-2-pyrrolidone + 1-hexanol + sodium chloride, + potassium chloride, or + potassium acetate at temperatures (283.15 and 323.15) K under atmospheric pressure. The liquid-phase splitting for the ternary system of water + N-methyl-2-pyrrolidone + 1-hexanol can be enhanced by adding the same percentage of salts (sodium chloride, potassium chloride, or potassium acetate), and the influence follows the order of sodium chloride > potassium chloride > potassium acetate. The experimental data were also compared with the values calculated by the electrolyte-NRTL model. In general, the model reproduces reasonably for the LLE phase diagrams.