The solubility of propylene in semicrystalline isotactic polypropylene (iPP) was measured at temperatures from (348.15 to 383.15) K and pressures up to 8 MPa by a pressure-decay method. The results demonstrated that solubility of propylene in iPP is increased with elevated pressure and decreased with elevated temperature. The results could be correlated using the Sanchez-Lacombe equation of state (SL EOS) with temperature-dependent binary interaction parameters k(ij) It was shown that the SL EOS can well predict the solubility of propylene in polypropylene over a wide range even above the critical temperature and pressure. The deviations between experimental data and calculated results were within 5 %. It is important to point out that the value of k(ij) varied almost linearly with respect to temperature, and the solubility of propylene in semicrystalline polypropylene in other conditions can be estimated.