High speed fracture behaviour of nylon 6/SEBS-g-MA blends with rather small rubber particles near the lower limit for rubber toughening is characterized by the standard Izod impact test and the Vu-Khanh methodology. This characterization expands on previous reports that have 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. Load-deflection curves and impact strength of blends with different rubber particle sizes, using both thick and thin specimens, are also reported. Load-deflection curves of tough blends do not show significant differences after normalization by specimen thickness. 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. All blends examined here show four different regions, i.e. an extensive shear yield zone, a shear yield zone, a cavitation zone and an apparent non-deformed zone within a visible whitened zone. Vu-Khanh parameters, fracture energy at initiation and tearing modulus, show a strong relation to the average rubber particle size and the deformed zone size.