Abstract An effective intumescent flame retardant (IFR) system, consisting of microencapsulated ammonium polyphosphate (MCAPP) and pentaerythritol (PER), was developed to improve the fire resistance of EPDM. The flammability of the IFR-EPDM composites was evaluated by limiting oxygen index, UL-94 test and cone calorimeter test. The cone calorimeter results showed that the peak of heat release rate and total heat release of IFR-EPDM composites decreased dramatically compared to that of neat EPDM. The thermal degradation behaviors of EPDM and IFR-EPDM composites were investigated using thermogravimetric analysis and real time Fourier transform infrared spectra. Moreover, scanning electron microscopy was utilized to explore the morphology of the char residues.