The BiFeO3 was used to intumescent flame retardant (IFR) polypropylene (PP) composites as a synergist. The limiting oxygen index (LOI) and UL‐94 tests indicated that there is an optimum synergistic concentration of BiFeO3 in the PP/IFR composites. Thermogravimetric analysis (TG) results of flame retardant PP showed that the moderate of BiFeO3 can reduce the decomposition rate of sample at high temperatures. TG of APP/PER/BiFeO3 showed that BiFeO3 main affects the third mass loss stage of APP/PER. So the morphology and composition of the char residue of APP/PER/BiFeO3 composites were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and laser Raman spectroscopy (LRS). An appropriate amount of BiFeO3 can react with APP/PER forming BiOP and FeOP bond, and so more P elements was involved in a crosslinking reaction to form more stable char residue, which can effectively increase the flame retardant properties of PP. POLYM. COMPOS., 38:2771–2778, 2017. © 2015 Society of Plastics Engineers