The thermal degradation mechanism of a novel polyvinyl alcohol/silica (PVA/SiO 2 ) nanocomposite prepared with self-assembly and solution-compounding techniques is presented. Due to the presence of SiO 2 nanoparticles, the thermal degradation of the nanocomposite, compared to that of pure PVA, occurs at higher temperatures, requires more reaction activation energy (E), and possesses higher reaction order (n). The PVA/SiO 2 nanocomposite, similar to the pure PVA, thermally degrades as a two-step-degradation in the temperature ranges of 300–450°C and 450–550°C, respectively. However, the introduction of SiO 2 nanoparticles leads to a remarkable change in the degradation mechanism. The degradation products identified by Fourier transform infrared/thermogravimetric analysis (FTIR/TGA) and pyrolysis-gas chromatography/mass spectrometric analysis (Py-GC/MS) suggests that the first degradation step of the nanocomposite mainly involves the elimination reactions of H 2 O and residual acetate groups as well as quite a few chain-scission reactions. The second degradation step is dominated by chain-scission reactions and cyclization reactions, and continual elimination of residual acetate groups is also found in this step.