Morphology, mechanical properties and fracture behavior of polypropylene/polyamide 6/ethylene polypropylene diene monomer graft maleic anhydride (PP/PA6/EPDM-g-MA) ternary blends containing various amounts of the EPDM-g-MA rubbery phase (from 0 to 9 wt%), with special attention to the structure-property relationships through the core-shell morphology development, were studied. The fracture surface, deformation micro-mechanisms and mechanical properties of the blends were examined using field emission scanning electron microscopy technique, tensile and impact tests, respectively. The fracture properties were characterized in detail by the linear elastic fracture mechanics method. The fracture energy (G(C)), fracture toughness (K-IC) and impact strength were improved monotonically up to some EPDM-g-MA content, above which the characteristics were appreciably enhanced. These results were attributed to an alteration of this morphology from dispersion of PA6/EPDM-g-MA core-shell particles at low EPDM-g-MA contents to the aggregated structure of core-shell particles at higher EPDM-g-MA contents. The micro-void formation via activation of internal cavitation or debonding of the rubbery phase was found to be responsible for the stress whitening phenomenon that occurred during the impact fracture process and, hence, increased impact toughness. Graphic abstract