Acrylonitrile-butadiene-styrene (ABS) resins with various rubber contents were prepared by applying nickel catalyzed high-cis polybutadiene rubber (BR9004) as toughening agent via bulk polymerization. The influence of rubber content and its characteristics on the morphology, mechanical properties, and fracture mechanisms of ABS resins were investigated. The relevant performance parameters were also evaluated and compared with a commercial injection grade resin (ABS-8434). The results show that each synthesized resin generally contains some irregular microsized particles with a certain amount of subinclusions besides the analogous 'sea-island' morphology to ABS-8434. The subinclusions considerably enhance the volume fraction of rubber phase; this leads to an increasing maximum loss tangent (tan delta) value, a decreasing storage modulus and glass transition temperature (T-g) of rubber phase. Besides, the higher grafting degree can not only produce a higher T-g of grafted copolymer but also improve the compatibility of rubber phase with matrix. Based on the performance measurements and fractography, the final product with a rubber content of 9.3% reveals ductile fracture behavior and excellent comprehensive properties far superior to ABS-8434 due to combined shear yielding and massive crazing. POLYM. ENG. SCI., 50:961-969, 2010. (C) 2009 Society of Plastics Engineers