A series of acrylonitrile-butadiene-styrene (ABS) copolymers were prepared using lithium-catalyzed low-cis rubber (PB700A), nickel-catalyzed high-cis rubber (BR9004), and their compounded rubber (PB700A/BR9004 = 50:50) as toughening agents through bulk polymerization. The effects of molecular structures of rubbers on the dissolving and grafting process of them were investigated. The structure and properties of ABS resins were characterized with FTIR, TEM, and performance measurements. It is shown that the characteristics of rubbers affect their dissolving state and grafting reaction and consequently influence the morphology and properties of ABS materials. BR9004 promotes the formation of irregular microsized rubber particles with special "salami"-like structure and, therefore, presents better mechanical properties. PB700A has much higher 1,2-isomers, which benefits its dispersion and grafting reaction; its toughening effect, however, is unsatisfactory and can be improved by the incorporation of BR9004. POLYM. ENG. SCI., 49:2249-2256, 2009. (C) 2009 Society of Plastics Engineers