Since Bueche, Graessley, Onogi, etc., advanced the concept of macromolecular entanglements, the subject has been studied extensively. So far, there are two kinds of methods of measuring the entanglements in a polymer system : One is the measurement of viscosity or other related properties of polymer fluids, either melts or solutions; the other is the measurement of modulus or other related properties of completely amorphous polymers. Until now, the effective method of measuring macromolecular entanglements for crystalline or semicrystalline polymers and fibers has not been developed. We report here a new method of measuring macromolecular entanglements of polymeric solids-using swelling differential scanning calorimetry (swelling DSC or SDSC), and we prove that the entanglements in fibers and polymeric materials can be measured quickly and conveniently with this method.