Reactive blending of 70 vol.-% polypropylene (PP) and 30 vol.-% polyamide-6 (PA-6) was performed in the presence of various amounts of succinic-anhydride-functional elastomers which are immiscible with both blend components. Characteristic morphological feature of the resulting multiphase polymer blends was a continuous polypropylene matrix containing dispersed core/shell microparticles with rigid polyamide-6 core and soft elastomer shell. Accumulation of the elastomer component at the polypropylene/polyamide-6 interface and reaction of the succinic anhydride of the elastomer with the amine-endgroups of PA-6 enhanced PA-6 dispersion and proved to be the key to unusual property synergisms. In contrast to the conventional soft maleic-anhydride-grafted EPM elastomer (EPM-g-MAH), the stiffer maleic-anhydride-grafted poly[styrene-b-(ethene-co-butene-1)-b-styrene] (SEBS-g-MAH) was much more efficient as blend compatibilizer and gave PP/PA-6 blends with greatly improved strength and toughness without sacrificing stiffness.