In this study, the effects of repeated extrusion on the mechanical properties, morphology, and interfacial tension of polypropylene (PP)/ethylene propylene diene monomer (EPDM) (80/20) blends were investigated. For the PP/EPDM (80/20) blends, the impact strength of the blends increased with repeated extrusion, which could be attributed to the interaction between the PP and the EPDM. The interfacial tension of the PP/EPDM (80/20) blends, which was determined using the Palierne and ChoiSchowalter models, decreased with an increase in the number of repeated extrusion. Based on the results of the mechanical properties and morphology, the interaction between the PP and the EPDM with repeated extrusion contributed to the reduction of interfacial tension between the PP and the EPDM, which consequently improved the impact strength of the PP/EPDM (80/20) blends. The results for the nuclear magnetic resonance studies supported the increase in impact strength of the PP/EPDM (80/20) blends with repeated extrusion. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013