A new copolymer of tris(2-methoxyethoxy) vinylsilane (TMEVS)-grafted ethylene-propylene-diene elastomer (EPDM-g-TMEVS) has been developed by grafting of TMEVS onto EPDM by using dicumylperoxide (DCP) initiator. The linear polystyrene blends (EPDM-g-TMEVS/PS) based on EDPM-g-TMEVS have been synthesized with varying weight percentages of polystyrene in a twin-screw extruder. In a similar manner, the dynamically vulcanized and nanoclay-reinforced polystyrene blends have also been developed using DCP and organically modified montmorillonite clay seperately by means of a twin-screw extruder. The grafting of TMEVS onto EPDM at allylic position present in the third monomer of EPDM has been confirmed by Fourier Transform infrared spectroscopy. The effect of silane-grafted EPDM and concentration of nanoclay on mechanical properties of polystyrene blends has been studied as per ASTM standards. The morphological behavior of these blends has been investigated using scanning electron microscope. It was observed that the incorporation of silane-grafted EPDM enhanced the impact strength and the percentage elongation of linear- and dynamically vulcanized blends. However, the values of tensile strength, flexural strength, flexural modulus, and hardness of the blends were found to be decreasing with the increase of silane-grafted EPDM. In the case of nanoclay-reinforced polystyrene blends, the values of impact strength, tensile strength, flexural strength, flexural modulus, and hardness were increased with an increase in the concentration of nanoclay. XRD studies have been carried EPDM-g-TMEVS/PS blends. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2859-2871, 2009