Particle-filled polymer composites are becoming attractive because of their wide applications and low cost. In this study, the effects of fillers such as mica and fly ash, at varying concentrations, on the mechanical, thermal, electrical, rheological, and morphological properties of polyester thermoplastic elastomer (Hytrel®) were investigated. Composites of Hytrel ® with varying concentrations (5-40 wt%) of mica and fly ash were prepared by twin screw extrusion. Mechanical properties, such as flexural strength and modulus, were found to increase with filler concentration. Mica showed a moderate increase in tensile strength with low concentrations, whereas the strength decreased with fly ash concentration. Thermal and electrical properties of the composites were found to increase with filler concentration. Morphological studies revealed that there was a good dispersion of filler in the polymer matrix at lower concentrations. © The Author(s), 2010.