The UNIFAC model is extended to the prediction of vapor-liquid equilibria of polymer solutions using a proposed relation between the volume parameter r(n) for an n-mer polymer and that r(1) for the monomer. The modified UNIFAC model does not require a free-volume term as does the UNIFAC-FV model. As a result, no additional information is needed for the vapor-liquid equilibria Eq. (1a) calculation of polymer solutions other than the original UNIFAC group parameters. For 51 binary polymer-solvent systems, the total average absolute deviation of solvent activities in polymer solutions was 6.8% for the modified UNIFAC model versus 7.4% for the UNIFAC-FV model and 18.7% for the original UNIFAC model.