The theological and tensile properties and the morphology of polypropylene(PP)/ethylene-propylene-diene terpolymer (EPDM)/ionomer ternary blends were investigated, using a rheometric dynamic spectrometer (RDS), a dynamic mechanical thermal analyzer (DMTA), a tensile tester, and a scanning electron microscope (SEM). Two kinds of poly (ethylene-co-methacrylic acid) (EMA) ionomers, neutralized with different metal ions (Na+ and Zn++), were used. Blends were melt-mixed, using a laboratory internal mixer at 190 degrees C. The composition of PP and EPDM was fixed at 50/50 by wt % and the EMA ionomer contents were varied from 5 to 20 wt %, based on the total amount of PP and EPDM. It was found that the ternary blends, containing Na-neutralized ionomer, showed considerably different theological properties and morphology as compared to the PP/EPDM binary blend, due to the compatibilizing effect of the ionomer for PP and EPDM, while the ternary blends, containing the Zn-neutralized ionomer, did not. The compatibilizing effect was most prominent at 5 wt % of ionomer concentration.