Polyamide 6/SiO2 (PA6/SiO2) nanocomposites with varying amounts of SiO2 were prepared by using a novel sol gel technique. These nanocomposites were formed in situ by hydrolysis and through the condensation of tetraethoxysilane (TEOS) using formic acid with a small amount of water as the solvent for PA6. Observations of TGA showed that the thermal stability of PA6 nanocomposite was significantly improved compared to that of neat PA6. Microstructure development during the thermally induced crystallization of PA6/SiO2 nanocomposites was investigated with a combination of differential scanning calorimetry (DSC), FTIR spectroscopy, scanning electron microscopy (SEM), and AFM. FTIR spectroscopy was used to determine the crystal form of these nanocomposites, and it was concluded that SiO2 nanopartides have the gamma-nucleating effect. The crystallinity of nanocomposites decreased with increasing TEOS loading as compared to that for neat PA6. SEM showed a very fine dispersion of nanoscale silica whereas SEM and Zetasizer proved the silica particle size was about 100-200 nm. The isothermal crystallization kinetics of these nanocomposites with increasing SiO2 content were investigated, and it was shown that the amount of SiO2 plays a significant role in crystallization kinetics.