Here, the physical properties of maleic-anhydride-modified styrene-ethylene-butylene-styrene copolymer (mSEBS) were controlled by adding paraffin oil; mSEBS formed the interface between polyamide 6 (PA6) and polystyrene (PS). Adding 50 wt% paraffinic oil to mSEBS enabled the reduction of the glass transition temperature (T-g) of the ethylene-butylene block and PS block. Change in T-g increased with the decreasing molecular weight of paraffin oil, indicating that the physical properties of mSEBS can be controlled. In this study, PA6/ mSEBS binary blends and PA6/mSEBS/PS ternary blends were prepared using high-shear kneading process. In the ternary blends, mSEBS forms a core-shell structure containing PS segment. In the PA6/mSEBS binary blends, the maximum notched Izod impact strength was 25.0 kJ/m(2), and in the ternary blend its value was more than 60.0 kJ/m(2), revealing significantly increased impact strength. The fracture surface of the binary blend exhibited the occurrence and expansion of many voids. In case of ternary blends, large plastic deformation was confirmed. Result of dynamic mechanical analysis (DMA) revealed a large loss tangent (tan delta) from - 90 to - 25 degrees C in the ternary blend, unlike in neat PA6 or the binary blends. The flexible mSEBS sandwiched between PA6 and PS in the core-shell structure preferentially deformed during deformation, which revealed that its characteristic relaxation behavior was activated. These results suggest that controlling the physical properties of the interface in a higher-order structure of a polymer blend may enable the efficient expression of the interfacial material's function.