The purpose of this study was to investigate contribution of nanoclays to the flame retardancy performance of a traditional brominated flame retardant compound with various combinations of antimony trioxide and zinc borate. The matrix polymer acrylonitrile butadiene styrene (ABS) was compounded by melt mixing in a laboratory size twin-screw extruder. X-ray diffraction analysis and transmission electron microscopy revealed that nanoclay silicate layers were mainly intercalated with certain level of exfoliation in ABS matrix. Flammability analysis investigated by mass loss calorimeter, limiting oxygen index, and UL-94 tests indicated that use of nanoclays improved all flame retardancy parameters significantly. For instance, the increase in the limiting oxygen index was up to 32% O 2, while the suppression in peak heat release rate value was as much as 82%, of course in each specimen the highest rating of V-0 in UL-94 test was obtained. Thermogravimetric and other residue analyses pointed out that these contributions were especially due to the condensed phase flame retardancy mechanism of nanoclay which contributes stronger and carbonaceous char formation acting as a barrier to heat and flammable gases and retarding volatilization via tortuous pathway. © 2012 Society of Plastics Engineers.