Polycarbonate nanocomposites filled with pristine and modified silica were prepared by simple melt compounding. The thermal degradation behavior of composites was investigated by thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC). To understand the thermal degra- dation mechanism, the chemical structures of gaseous and solid degradation products were detected by thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. KissingereAkahiraeSunose (KAS) and FlynneWall eOzawa (FWO) methods were employed to analyze the thermal degradation kinetics. High thermal degradation temperature was obtained by incorporating both types of nanoparticles into matrix, but the maximum mass loss rate increased. According to the DSC curves for degradation process, the change of the number and position of absorption peaks meant that the degradation mechanism of composites was different from that of neat Polycarbonate. The analysis for TGA chars confirmed the presence of alcoholysis reaction between Polycarbonate and silica nanoparticles during the thermal decomposition. TGA/FTIR results proved that no new degradation volatiles were produced during the thermal degradation of composites, but the total amounts of all gaseous products decreased by adding silica nanoparticles. The degradation activation energies of both composites increased significantly relative to neat Polycarbonate, especially for the composite with modified silica.