The distribution of maleated styrene-hydrogenated butadiene-styrene (mSEBS) elastomer and nano-SiO2 in nylon 6 matrix was controlled by varying the blending procedure. Nano-SiO2 particles with different surface properties (hydrophilic versus hydrophobic) were adopted to adjust their interactions with other components. Two different structures, separate dispersion of nano-SiO2. and elastomer particles as well as encapsulation of nano-SiO2 fillers by the elastomer, were obtained. The structured were confirmed through scanning electron microscope (SEM) investigation. The mechanical measurement results showed that the microstructure and the interactions among the components had dramatic influences on the final mechanical properties, especially Izod fracture toughness, for the ternary nanocomposites. The nanocomposites containing hydrophilic nano-SiO2 had better mechanical Performances compared with the composites filled with hydrophobic SiO2 when they were in the same microstructure. The nanocomposites with separate dispersion structure showed higher stiffness compared with those of encapsulation type. However, the separately dispersed nano-SiO2 particles restricted the cavitation of elastomer phases that led to low toughening effectiveness. The difference of cavitation intensity for elastomer phase was revealed by SEM investigation on the facture surfaces for the nanocomposites with the two different microstructures. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 469-479, 2010