This study covers the preparation and characterization of perlite-filled polypropylene (PP). The compositions of 15, 30, and 50 % by weight perlite-PP composites were prepared by melt-mixing. The PP used in this study was either applied in the virgin form or gamma -irradiated in air at the doses of 10, 25, 50, and 100 kGy to determine the effect of oxidative degradation in composite properties. Furthermore, the active sites containing oxygen produced by gamma -irradiation in PP may provide a possible enhancement by the interfacial interaction between perlite and PP. An initial sharp drop in torque readings during the melt-mixing of perlite-PP composite preparation indicated an extensive chain scission and degradation by gamma -irradiation. The thermal properties of the composites were characterized by DSC. The ultimate tensile strength and elongation and also impact strength decreased in all composites with gamma -irradiation. Yet, these changes appeared not to be faster than was the change in unfilled PP upon irradiation. Scanning electron microscopy revealed an interfacial adhesion between perlite and irradiated PP while virgin PP did not show any evidence of adhesion. (C) 2001 John Wiley & Sons, Inc.