An equation of state (EOS) recently proposed by the present authors based on the nonrandom lattice fluid theory was applied to correlate phase equilibrium properties of polymer solutions. The EOS requires only two molecular parameters for pure r-mers and one additional interaction energy parameter for binary systems. The molecular parameters for 12 common polymers and the binary interaction energy parameters for 17 common binary polymer solutions are presented. We round that the EOS describes quantitatively well the solvent activities and heats of mixing of various polymer solutions. The results obtained with the EOS is compared with the results obtained by such models as the random lattice model (Okada and Nose, 1981a, b), Flory theory (Flory, 1970) and the EOSs proposed by Sanchez and Lacombe (1976) and Panayiotou and Vera (1982) and UNIFAC-FV model (Oishi and Prausnitz, 1978). We believe that the result obtained to date demonstrated that the EOS can be a useful tool for practical phase equilibrium calculations of polymer solutions.