A muscovite/boron phenol-formaldehyde composite is prepared by compression moulding. After 10 min pyrolysis at 1000°C, it was still stable with a thermal residue value of 77.8%. The surface of the thermal residue was covered by shell-like coatings that may protect interior materials from further oxidation and decomposition, according to the scanning electron microscope and energy dispersive X-ray investigations. Also, a thermogravimetry analysis study showed that the muscovite/boron phenol-formaldehyde composite has much higher heat-resistance than pure boron phenol-formaldehyde. In addition, X-ray photoelectron spectroscopy characterisation suggested that the percentage of carbon in the thermal residue exceeded in the muscovite/boron phenol-formaldehyde composite. This suggested that most of the carbon was reserved and the carbon framework was well protected. Further analysis revealed that nearly half of the boric oxide, alumina and silica in muscovite/boron phenol-formaldehyde composite were reduced to boron nitride, aluminium and silicon carbide, respectively, after the pyrolysis.