A series of low-cis-1,4/high-cis-1,4 polybutadiene composite rubber toughened poly(acrylonitrile-butadiene-styrene) (ABS) terpolymers were prepared and characterized. The morphological analysis shows that specimens exhibit common characteristics of two single rubbers while mechanical measurements reveal that better comprehensive properties can be obtained as more Ni-9004 blended in composite rubber. When increasing Ni-9004/Li-700A ratio, one brittleductile transition occurs at 5.0 wt % rubber usage and three transition regions exist under 10.0 wt % usage. In addition, the characteristic forcetime curves and fractography demonstrate that failure behavior and crack propagation mode can be effectively evaluated. Conclusively, quasi-brittle fracture can be seen for specimens with obvious cavitation and matrix stripping followed by riverlike fibrous and periodical Wallner stripes, whereas ductile fracture is observed for those with alternate parabolic and firework patterns accompanying stress-whitening and ligament-forming progress. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013