This work reports migration and distribution of the plasticizer of PVB phase during processing of the PP/waste PVB blends. Storage modulus of the blends and glass transition temperature of the PP and PVB phases revealed that some part of the plasticizer of the waste PVB migrated to PP matrix and interface. This observation was further investigated from thermodynamic points of view. The calculations of solubility parameter, surface tension, and interfacial tension for the blend components helped to interpret the migration phenomenon. The obtained data confirmed relative tendency of the plasticizer to migrate to PP phase and interface. Furthermore, the effects of plasticizer migration on behavior of the blends were studied. It was shown that plasticizer can significantly affect the rheological properties of the compatibilized PP/PVB blends.