The high speed fracture characterization of various nylon 6/SEBS-g-MA and nylon 6/EPR-g-MA blends by the standard Izod impact test and the Vu-Khanh methodology is reported. This characterization provides a more in-depth examination of the influences of nylon 6 molecular weight and rubber types on fracture behaviour, expanding on a previous report that examined the standard Izod impact strength of nylon 6 blends with various maleic anhydride grafted styrene-(ethylene-co-butylene)-styrene (SEBS-g-MA) materials including the ductile-brittle transition behaviour that occurs when the rubber particle size and the test temperature are varied. Morphological features near crack tips formed at high speed were examined by microscopy to gain insight about the sequence of events that occur during crack propagation. This study has shown a linear relationhip between toughness parameters versus the deformed zone size for all the blends. This suggests that the energy absorption for these rubber-toughened blends stems mainly from plastic deformation of the matrix which is induced by rubber cavitation. TEM observations of the region near the crack tip show that the extent of rubber particle cavitation depends on the nylon 6 matrix molecular weight.