Densities and viscosities of aqueous solutions of polyethylene glycol 4000 mass fraction from (5 to 50) % have been measured at different temperatures, (298.15, 303.15, 308.15, 313.15, and 318.15) K. The density data show a linear variation with mass fraction of the polymer for all temperatures. The viscosity data of PEG 4000 solutions were correlated as a function of mass fraction, using a nonlinear equation, for the five different temperatures covered in the present work. Densities, viscosities, and liquid - liquid equilibria of polyethylene glycol - sodium citrate two-phase systems have been measured and are correlated with compositions at (298.15, 308.15, and 318.15) K. The effect of tie line lengths on density and viscosity of the aqueous two-phase systems has also been represented. The tie lines were correlated using the Othmer - Tobias and Bancraft equations as well as the virial equation. The coefficients were estimated and reported. The mean deviations between the experimental and calculated equilibrium compositions in the top and bottom phases were < 1 %. © 2009 American Chemical Society.