The phase diagrams and compositions of coexisting phases have been determined and correlated for poly(ethylene glycol) (PEG) 3000 + trisodium citrate aqueous two-phase systems (ATPS's) at 25 degrees C and different pH values (6.1, 7.5, and 9.0). It was found that an increase in pH caused the binodal curve to be displaced downward and also the expansion of the two-phase region. The experimental binodal data of the mentioned system has been successfully correlated with Bleasdale equations (high R-2 and low AARD). Furthermore, the viscosities, densities, electrical conductivity, and refractive index of binary (PEG 3000 + water; trisodium citrate + water) and ternary (PEG 3000 + trisodium citrate + water) systems at the above pH value have been measured and correlated. The density data show a linear variation with mass fraction of the polymer and also the salt. The viscosity data of PEG 3000 solutions were correlated as a function of mass fraction, using a nonlinear equation. The effect of tie line lengths on density and viscosity of the aqueous two-phase systems has also been represented.