Impact properties of perlite-filled high-density polyethylene (HDPE) composites were studied with the Charpy method by using both notched and unnotched samples. gamma-Aminopropyltriethoxy silane (gamma-APS, A-1100) was used as a silane coupling agent to improve the interfacial adhesion. The influences of the molecular parameters of HDPEs, molecular weight, degree of branching, degree of crystallinity, and also the effect of gamma-APS on the impact properties are represented in this work.