The dispersive mixing of premixed nano-size untreated and treated silica particles, and compounds in ethylene-propylene-diene terpolymer (EPDM) were studied using an ultrasonic extruder (Ultra) and compared with an internal mixer (Int) processing. The rheological properties and extrudate swell of the compounds were investigated and compared with carbon black filled compounds. The Ultra processing broke down the silica agglomerate sizes effectively, which became smaller than after an Int processing. The silane treated silica exhibited a considerable reduction in the agglomerate sizes compared to the untreated silica in an Int. These results were then compared with carbon black filled compounds. The viscosity of the compounds with untreated and treated silica was higher than the compounds with carbon black. This may be due to the rough surface of the silica particles. The silane treated compounds exhibited a lower viscosity than the untreated compounds. The effect of extrudate swell reduction was minimal on the treated compounds.