In this article, the effect of silk fibroin nanofibers as a toughening agent of carbon fiber/fabric-reinforced epoxy composites is experimentally investigated. The composites showed up to 30% improvement in Mode II fracture toughness at 0.1 wt% of silk fibroin nanofibers content. The scanning electron microscopy observation revealed that the fracture surface of silk fibroin nanofibers modified carbon fiber/fabric-reinforced epoxy composites appearance of the broken fiber and the ductile-like matrix cracks showed a good adhesion between matrix resin and carbon fibers, which are reasons for the enhanced mode II interlaminar fracture toughness. [GRAPHICS] .