A Gamma-ray irradiation was employed to modify high density polyethyelene (HDPE) in order to impart poor interfacial interaction between hydrophobic matrix and hydrophilic Sericite-Tridymite-Cristobalite (STC) filler. The STC filler was further treated with a silane coupling agent. The FTIR, SEM and rheological observations confirmed enhanced interactions between oxygen containing groups on the irradiated matrix (c-HDPE) and NH 2 groups of silane-treated filler (t-STC), resulting in improved mechanical properties of the composites (10 times in case of impact strength). The parameter of the theoretical model used characterizing interfacial interaction increased from 2.69 for HDPE/STC up to 4 for irradiated and surface treated material.