The influence of autoclaving on the properties of silk fibroin fabrics (SF(fab)s) was evaluated. High-performance liquid chromatography revealed that the molecular weight (Mw) of the fibroin molecule in SFfabs decreased as the treatment temperature and time increased, which suggests that the fibroin molecule in the fabrics was thermal degraded. Additionally, differential scanning calorimetry experiments revealed a shift of the endothermic peak to higher temperature with increasing treatment temperature and time, which indicates an improvement in the thermal stability of the fibroin molecule in the autoclaved fabrics. Furthermore, C-13 cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) analysis revealed that the intensity ratios for the beta-sheet and random-coil peaks fluctuated during autoclaving. The NMR analysis also revealed the presence of an unknown structure in the autoclaved SF(fab)s under certain conditions. The changes in the Mws and degradation temperatures for the autoclaved SF(fab)s are assumed to be induced by the structural changes observed via NMR. Consequently, autoclaving is considered to be an effective technique for modifying the secondary structure and properties of SF(fab)s with high beta-sheet contents using only water and heat without added reagents. (C) 2014 Elsevier Ltd. All rights reserved.