Abstract: The silk fibroin (SF) and Poly (butylene succinate) (PBS) were respectively dissolved in 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol (HFIP) to fabricate SF/PBS hybrid composite ultrafine fibrous membranes of different mass ratios by electrospinning. The hybrid composite ultrafine fibrous membranes prepared by using different mass ratios of SF and PBS were treated by methanol, The morphology of membranes were observed by field-emission scanning electron microscopy (FE-SEM). The structure and mechanical properties were characterized by means of FTIR, XRD, and Instron 5543 tensile tester. The results show the morphology of hybrid ultrafine fibers with different mass ratio was similar and uniform. Mechanical properties and the crystallinity of the hybrid composite ultrafine fibrous membranes are increased with the addition of PBS. when the hybrid mass ratio increases from 90/10 to 50/50, failure strength increases from 15.2MPa to 17.3MPa and failure elongation increases 2.1% to 38.2%. Compared with electrospun silk fibroin ultrafine fibrous membranes, hybrid composite ultrafine fibrous membranes show good mechanical properties.