Flammability of polypropylene / ethylene-propylene-diene copolymer (PP/EPDM) filled with melamine phosphate (MP) and pentaerythritol phosphate (PEPA) was studied by limiting oxygen index (LOI), UL 94, and cone calorimetry. The thermal degradation of the composites was investigted using thermogravimetric analysis (TG) and real-time Fourier transform infrared spectrum (RT-FTIR), and the mechanical properties of the materials were also studied. It had been found that the PP/EPDM/PEPA/MP composites (PEPM series) showed better flame retardancy than that of the PP/EPDM composites containing MP or PEPA. TG and RT-FTIR Studies indicated that the interaction occurs among MP, PEPA, and PP/EPDM. The incorporation of the flame retardants deteriorated the mechanical properties of the materials. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3804-3811,2008