The fracture surfaces and deformation micromechanisms of styrene-co-acrylonitrile (SAN)/polybutadiene-g-styrene-co-acrylonitrile (PB-g-SAN) blends with the compositions ranging from 65/35 to 0/100 were studied with a scanning electron microscopy technique. The results were compared to the essential work of fracture parameters obtained in a previous study conducted on double-edge notched tension specimens. Different plastic damage mechanisms were observed, and they depended on the blend composition. For blends of 65/35 and 45/55, a high degree of rubber particle cavitation and multiple cracking followed by the massive shear yielding of the matrix were found to be the main source of energy dissipation during crack growth. Within this compositional range, more intense plastic damage in a larger volume of material, especially at the notched region, was observed as the concentration of the rubbery phase increased. For the 25/75 blend, the prevailing mechanism was pure shear yielding without any sign of cavitation inside the particles, and the fracture surface became relatively flat and was covered with aligned small microcracks. This sample showed the highest specific essential work (we) value among the blends examined in the previous study. For the samples containing concentrations of dispersed phase higher than 75%, the shear yielding process gradually became less important with the progressive importance of multiple crazing so that high-magnification micrographs revealed extensive microcracking/crazing both inside and between the rubber particles, as the only active deformation micromechanism for neat PB-g-SAN. The variation we and specific plastic work of fracture with the PB-g-SAN phase content were successfully explained in terms of prevalent deformation mechanisms. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40072.