Influence of compatibilizer on morphologies and mechanical properties for polypropylene/high

impact polystyrene/compatibilizer blends was investigated. Three types of poly（styrene-block-poly（ethylene-butene）-block-polystyrene triblock copolymer（SEBS）used as compatibilizer have differentratio of styrene/ethylene-butene（R）. SEBS volume fraction（φ_e）was from 0.05 to 0.3. On morphologies of the polymer blends, R influenced diameter of dispersed phase. Also, in case of small R,impact strength of the polymer blends was improved at little until φ_e ＝0.1. And, the impact strength of those was improved remarkably with φ_e above 0.15. On the other hand, in case of large R, impact strength was improved at little as well as in case of small R until φ_e＝0.1. However, the impact strength was unimproved with φ_e above 0.15. In case of small R, elastic modulus and tensile yield stress of thepolymer blends were decreased. However, in case of large R, those were maintained highly.