The simplified mixing rule for the Peng-Robinson EOS parameters proposed by Ahlers and Gmehling has been extended to calculate the VLE behavior of polymer solutions. To avoid the calculation of the molar volumes in the mixing rule as required in the UNIFAC-FV model, the quadratic mixing rule for parameter b has been modified to take into account the free volume contribution to the excess Gibbs energy for the solvent-polymer solutions. The group interaction parameters and relative van der Waals surface area parameters of the original UNIFAC model are used for the calculations. Satisfactory predictions are obtained for 18 solvent-polymer systems, which cover a wide range of molar mass of the polymers. Additionally, activity coefficients at infinite dilution based on weight fraction for 36 systems have been calculated. The results of this paper show that the presented mixing rule results in a simple, predictive model with satisfying accuracy for the application in industrial process design.