Composites of serpentine and polypropylene (PP) were prepared by twin-screw extrusion. Serpentine was collected as rocks from the Ankara-Beynam region and ground into powder with an average particle size of about 3 lm for composite production. Both asreceived (rock) and powdered serpentine were characterized. A silane coupling agent (SCA), c-aminopropyl triethoxy silane, was used for the surface treatment of serpentine. Mechanical properties of the composites were measured in terms of impact strength, elastic modulus, stress at yield, stress at break, and percentage strain at break. The addition of serpentine was found to have a profound effect on the reinforcement of the PP matrix. Because of the stronger interactions at the interphase induced by SCA treatment, mechanical properties were improved further in comparison with the untreated composites. Similar thermal and morphological behaviors were recorded for the composites with and without surface treatment. Thermal studies showed an increase in both melting temperature and percentage crystallinity of the composites. Scanning electron microscopy analysis revealed that homogeneous distribution of filler was observed at low filler contents, but a certain extent of agglomeration was also seen at high filler loadings. V C 2011