Abstract: EPDM/PS alternative multilayer composites were prepared by micro-or nano-layer coextrusion system designed in this lab. The results of polar light microscope (PLM) and scanning electrical microscope (SEM) analysis indicate that the composites have the alternative multilayer structure. Compared to conventional blends, the fracture behavior of EPDM/PS alternative 64-layer composites is much different, which includes two stages: the PS layers break first, followed by only the EPDM layers elongated. Because both PS and EPDM layers are continuous and EPDM layers prevent the cracks or crazes developing between the nearby PS layers, the tensile strength and the Youngs modulus of the 64-layer composites are higher than those of the corresponding conventional blends. The effects of SEBS as a compatibilizer added into PS phase on the mechanical properties of EPDM/PS alternative multilayer composites were investigated. The results indicate that the interfacial adhesion strength between EPDM layers and PS layers and the toughness of the PS layers are improved in the presence of SEBS.