A novel charring agent, poly(p-propane terephthalamide) (PPTA), was synthesized with terephthaloyl chloride and 1,2-propanediamine through solution poly-condensation at a low temperature. PPTA was used together with ammonium polyphosphate (APP) to prepare a novel intumescent flame retardant (IFR) for an acrylonitrile butadiene styrene (ABS) resin. The flammability and thermal stability of the IFR ABS composites were investigated with limiting oxygen index, UL 94 vertical burning, and thermogravimetric analysis tests. The results showed that the IFR system had excellent flame retardancy and antidripping properties for ABS. The thermogravimetric curves suggested that there was a distinct synergistic effect of PPTA and APP, and this effect greatly promoted the char formation of the IFR ABS composites and hence improved the flame retardancy. Additionally, the structure and morphology of char residues were studied with Fourier transform infrared and scanning electron microscopy. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 968-973, 2011