In a systematic manner, the roles of MWNTs as filler and styrene acrylonitrile copolymer-graft-maleic anhydride (SAN-MA) as compatibilizer, individually and together, on dynamic-mechanical behavior of polycarbonate (PC)-rich/acrylonitrile butadiene styrene terpolymer (ABS) blend were studied. The investigations were performed using small-scale mixing in a one-step procedure with a fixed MWNTs content of 0.75 wt% and a blend composition of PC/ABS = 70/30 w/w. PC/SAN blends and nanocomposites as simpler model system for PC/ABS were also studied to reveal the role of the rubbery polybutadiene (PB) fraction. It is found that the tendency of MWNTs to localize within the PC component in compatibilized PC/ABS was lower than in compatibilized PC/SAN blends. Dynamic mechanical analysis (DMA) revealed the dual role of SAN-MA as blend compatibilizer and also promoter of MWNTs migration towards PC, where SAN-MA to MWNTs weight ratio varied between 1 and 4. At the compatibilizer/MWNTs weight ratio of 1, MWNTs localized in PC component of the blends whereas increasing the compatibilizer/MWNTs ratio to 4 led to migration of MWNTs toward SAN or ABS component. In DMA studies, loss modulus normalization of the nanocomposites revealed the coexistence of mobilized and immobilized regions within the nanocomposite structure, as a result of MWNTs and compatibilizer loading. POLYM. ENG. SCI., 54: 2696-2706, 2014. (C) 2014 Society of Plastics Engineers