Relation between impact and mechanical properties and morphology of polypropylene (PP)/elastomer/filler ternary composite was investigated. Polystyrene-block-poly(ethylene-butene)-block-polystyrene triblock copolymer (SEBS) or carboxylated SEBS (C-SEBS) was used as elastomer and calcium carbonate (CaCO3) having mean size about 160 nm was used. In the PP/SEBS/CaCO3 ternary composite, CaCO3 particles and SEBS particles were dispersed in the PP matrix separately. In the PP/C-SEBS/CaCO3 ternary composites, CaCO3 particles were embedded in C-SEBS, namely the core-shell particles were formed at lower CaCO3 concentration. However, some CaCO3 particles were dispersed directly in PP matrix at higher CaCO3 concentration. In order to clarify the influence of morphology, the measured modulus and tensile yield stress were compared with the predicted values by some prediction laws. In the PP/SEBS/CaCO3 composite, the impact strength increased with the amount of incorporated CaCO3 particles. Whereas, in the PP/C-SEBS/CaCO3 composite, the impact strength increased dependent on the amount of CaCO3 particles dispersed directly in PP matrix. From the observation of fractured surface, it was found that the impact strength is strongly affected by the morphology and dispersibility of CaCO3 particles. (C) Koninklijke Brill NV, Leiden, 2011