The adjuvant of organic bentonite (OBT), zinc oxide (ZnO), zeolite 4A (4A), aluminum phosphinate (AlPi), terephthaloyl-biscaprolactam (TBC), 2,2'-bis(2-oxazoline) (BOZ), and manganese dioxide (MnO2) on flame retardant enhancement of acrylonitrile-butadiene-styrene copolymer (ABS)/polyamide 6 (PA6)/styrene-maleic anhydride (SMA)/ammonium polyphosphate (APP) blends were investigated by using the limiting oxygen index (LOI), the UL-94 (vertical flame) test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The LOI datas and vertical flame tests showed that the synergistic flame retardant effect of OBT, ZnO, 4A, AlPi, BOZ, and MnO2 on the ABS/PA6/SMA/APP blend was good, and the LOI value of ABS/PA6/SMA/APP/MnO2 (55/15/5/25/2) system was 33% and class V-0 of UL-94 test was passed. The TGA data demonstrated that the incorporation of adjuvant was known to improve the fire properties essentially accompanied by only minor changes in thermal decomposition. The strong influence of oxygen on the thermal degradation of the ABS/PA6/SMA/APP system, and the oxygen could modify the carbonaceous structure. The microstructures observed by SEM indicated that the adjuvant can promote formation of compact intumescent inorganic-carbonaceous char layers in ABS/PA6/SMA/APP blends. Furthermore, the effects of adjuvant on the mechanical properties of ABS/PA6/SMA/APP blends were also investigated. The Izod impact strength of the ABS/PA6/SMA/APP/Adj composite showed a little depressing. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 1552-1560, 2010