Medified PS/clay-nanocomposites were prepared by SBS block copolymer and metallocene ethylene octene copolymer (m-EOC) through melt compounding. As to the results, toughness and impact properties of the SBS based blends were higher than that of those based on m-EOC due to the better miscibility of SBS and PS matrix. The results indicated a significant development in mechanical properties of the nanocomposite contained 1 w% of clay nanoparticles. X- Ray analysis showed only intercalated structures for the nanocomposites. As to the results, Scanning electron microscopy (SEM) showed a homogenous morphology for the nanocomposites and nanoclay particles were finely dispersed in the PS matrix. However, small agglomerations could be found in the nanocomposite included 3 w% of nanofillers. Energy dispersive X-ray (EDX) analysis was also demonstrated a proper distribution of Si elements from nanoclay in the nanocomposites. Thermal stability of the nanocomposites was also studied by heat deflection temperature (HDT) and thermo gravimetric analysis (TGA). It was found that an improvement in thermal degradation for the nanocomposite which was contained 1 w% of nanoclay.