A hydrophobic bombyx silk achieved by sol coating is characterized. The agent was firstly prepared by Dodecafluoroheptyl-propyl-trimethoxylsilane（DFS）hydrolysis, then through a sol–gel process, it coated and gelled on the fiber surface with lower surface free energy using bombyx silk fabrics as a substrate. The results of the wide-angle X-ray diffraction measurements (WAXD), TGA and DTG indicated that the thermal stability of the modified fiber was improved with the sol introduction. Scanning electron microscopic analysis (SEM) showed the morphology of the fibers in detail. The results indicated that the treated textiles had excellent water repellent property and water contact angle (CA) increased to 120.2 o.