The breakdown rates of filler agglomerates, compounded in ethylene-propylene-diene terpolymer (EPDM) matrix, were compared using silica, carbon black, calcite, talc and zinc oxide in an internal mixer (Int). The shear viscosity and the extrudate character were used for investigation. Small sized silica agglomerates were the most difficult particle to disperse. The small silica particle filled EPDM system exhibited the highest viscosity level. The quality of the extrudate smoothness improved, but the magnitude of the swell d/D decteased with small size particles. Among the fillers used, the zinc oxide exhibited the poorest character in the extrudate quality.