Abstract: Reactive core-shell modifiers of ABS-g-MA and ABS-g-AA were synthesized to toughen PA6. The difference between the modifiers lays in the reactive monomers on the shell, which would induce different interface properties between the PA6 blends. So the brittle-ductile transition and fracture behavior of the blends were studied when the other parameters were the same. Molau test and torque results indicate ABS-g-MA/PA6 shows superior interface strength. TEM shows ABS-g-MA and ABS-g-AA modifiers disperse in PA6 matrix uniformly. Mechanical test shows brittle-ductile transition takes place between 25%~30% modifiers mass fraction for ABS-g-MA/PA6 blends and impact strength more than 900 J/m is achieved, however, brittle-ductile transition takes place between 30%~35% modifiers mass fraction for ABS-g-AA/PA6 blends. Fracture mechanisms display cavitation of rubber particles and shear yielding of matrix are the major deformation mechanisms for ABS-g-MA/PA6 blends, however, no cavitation can be found and shear yielding is indistinctive for ABS-g-AA/PA6 blends. Vu-Khanh test shows ABS-g-MA/PA6 blends have much higher  G_i  value and toughness due to the higher interface strength.