The effects of different fillers on physical, mechanical, and optical properties of styrenic-based thermoplastic elastomers were investigated by experimental study. Poly[styrene-b-(ethylene-co-butylene)-b-styrene] block copolymer (SEBS)-based thermoplastic elastomer composites were prepared in a co-rotating intermeshing twin-screw extruder, using silica and calcite as filler materials with three different particle sizes. The loading ratios in the composites were varied. Hardness, density, tensile strength, tear strength, compression set, wear resistance, transmittance, and haze measurements were performed. Thermal properties and morphological structure were investigated by differential scanning calorimeter (DSC) and scanning electron microscopy (SEM), respectively. The results show that, an interaction between silica and the polymer matrix exists, whereas calcite does not show any interaction with the polymer. Therefore, it is concluded that, calcium carbonate can be used in the composite as filler for cost efficiency, whereas silica can be used as reinforcing material in SEBS-based thermoplastic elastomer composites, when optical properties are also concerned. POLYM. ENG. SCI., 50:677-688, 2010. (C) 2009 Society of Plastics Engineers