The pyrolysis of pure phenol-formaldehyde (PF) resin and boron carbide (B4C) modified PF resin was investigated by using thermogravimetry (TG) and pyrolysis gas-chromatography-mass-spectrometry (PY-GC/MS). Scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) spectroscopy were also employed to investigate the micro-structural evolution. It was shown from the TG analysis that the char residues Of pure PF resin were 62.9 and 60.5% after being pyrolyzed at 700 and 1000 degrees C. respectively. The degradation and failure of the resin matrix were mainly resulted from the release of volatiles. The phenol and its methyl derivates took a large proportion in the amount of volatiles. In comparison with the pure PF resin, the char residues of B4C modified PF resin were obviously higher, with the values of 71.9 and 68.4% at 700 and 1000 degrees C, respectively. Due to the oxidation-reduction reactions between B4C additive and oxygen-containing volatiles including CO and H2O, partial carbon and oxygen elements in the volatiles remained in the resin matrix in the forms of amorphous carbon and B2O3, respectively. The results of SEM and FT-IR characterization demonstrated the occurrence of the modification, and the amorphous carbon existed in the form of reticular substance. In addition, the amount of the released phenol and its methyl derivates was also decreased drastically due to the formation of borate. (C) 2009 Elsevier B.V. All rights reserved.