In this work, a new synergistic charring agent of melamine cyanurate-fumed silica (MCA-SiO2) has been synthesized through the facile self-assembly process, where melamine (ME) and cyanuric acid (CA) reacted and deposited on the fumed silica in the aqueous suspension. Then GF-PP/IFR-(MCA-SiO2) composites were prepared by melting blend of GF-PP and IFR containing MCA-SiO2. The general properties of the resulting composites were characterized by Cone calorimeter test (CCT), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) etc. Results show that the addition of SiO2 could greatly reduced the heat release rate (HRR) of the GF-PP/IFR-MCA composites and improved the flame retardant properties during burning. When the content of SiO2 in MCA-SiO2 was 20 wt%, the flame retardant property of the composites reached the UL-94 V-0 rating, corresponding to a the limiting oxygen index (LOI) of 32.4 %. This enhanced flame retardant property could be attributed to the fact that the fumed silica with low thermal conductivity could prevent the heat exchange, and assist in the formation of compact and dense char during the burning.