The first purpose of this study was using micro-composite approach by investigating the effects of micron-sized zinc borate (ZB) on the flammability behavior of ABS when used with and without a traditional brominated flame retardant (BFR) / antimony trioxide (AO) system. The second purpose was using nano-composite approach by investigating the contribution of nanoclays (NC) to the flame retardancy performance of the same systems. Flame retardancy of the specimens was investigated by Mass Loss Cone Calorimeter, Limiting Oxygen Index measurements and UL-94 vertical burning tests. Studies indicated that flame retardancy parameters were kept when AO were replaced with ZB while use of nanoclays improved all parameters significantly. Residue analyses revealed that predominant flame retardancy mechanism of traditional system was gas phase action, while ZB especially acts in the condensed phase by forming thicker and stronger char layer. Nanoclays further contribute to the formation of stronger and carbonaceous-silicate char acting as a barrier to heat and flammable gases and retarding volatilization via tortuous pathway.