The polystyrene/styrene-ethylene/butylene-styrene composites were prepared by melt blending process in this paper. The mechanical properties of PS/SEBS composites were analyzed. The results showed that the impact strength of PS/SEBS composites could be increased with the content increasing of SEBS, meanwhile the tensile strength was lower than pure polystyrene. When the content of SEBS increased to 13 wt.%, the impact strength of PS/SEBS composites was 2.4 times higher than that of pure PS. The fractured surfaces of the specimens were characterized by scanning electron microscopy(SEM). The results showed that the impact fractured surfaces produced a lot of sliding along with the addition of SEBS. The particles of SEBS could be well dispersed in polystyrene matrix. From rheological properties studies and the values of the torque, it was suggested that the maximum torque of PS/SEBS composites decreased drastically.