The effect of temperature on the densities and viscosities of aqueous solution of poly(acrylic acid) (PAA) of different mass fraction (from 0.05 to 0.50) and liquid-liquid equilibrium, densities, and viscosities for the aqueous two-phase PEG-6000 + PAA + water system at equilibrium have been measured. The densities and viscosities of the PAA + water system at different temperatures were correlated as a function of mass fraction. The binodal curves for the PEG + PAA + water system have been correlated using a four-parameter equation. The increase in temperature results in an increase in the two-phase region. The tie line compositions have been fitted to both the Othmer-Tobias and the Bancroft equations. A linear dependency of both the plots indicates the consistency of the data; however, the Bancroft equation gives the best fit.