The liquid liquid equilibrium for the mixtures of poly(ethylene glycol) (PEG) with mass -average molar of 4000, 6000, or 10 000 g mol(-1) + sodium hydrogen sulfite (NaHSO3) + water systems has been determined experimentally at T = 288.15, 298.15, 308.15, and 318.15 K. The temperature, PEG mass molar, mixture composition, and nature of anion effects on phase equilibrium were studied. The binodal curves at different temperatures were fitted to an empirical equation that correlates the concentrations of polymers and salt. The consistence of experimental data of equilibrium was available through of the Othmer-Tobias and Bancroft equations, and the parameters were reported.