Incorporation of SRF and ISAF grades of carbon black and precipitated silica improves the physical properties of the zinc stearate plasticized ionomer, namely, the zinc salt of sulfonated maleated EPDM rubber, which behaves as an ionic thermoplastic elastomer. The reinforcing ability of the fillers follows the order SRF carbon black < silica < ISAF carbon black. The activation energy of the melt flow also follows the same order. The results of infrared spectroscopic studies and dynamic mechanical studies reveal that, apart from the rubber-filler bonding, as is normally observable in diene rubbers, ion-dipole and hydrogen-bonding interactions occur between the active sites on the filler surface and the ionic aggregates.