Abstract: Poly(butylene succinate) (PBS)-silk fibroin (SF) core-shell composite ultrafine fibrous membranes were successfully fabricated by coaxial electrospinning and characterized by FE-SEM and TEM, and the fibrous membranes morphologies prepared at different inner flow rates of spinning were observed.The structure, crystallinity and mechanical properties of the composite ultrafine fibrous membranes before and after treatment with methanol were characterized by means of FTIR, XRD and tensile tester.The results indicate that the typical core-shell structure could be found from observing SF shell layer, PBS core, and the cross-section of the fibers.The average diameter of the core-shell composite ultrafine fibers increases with the increasing of the inner flow rate of spinning.After being treated with methanol, the molecular structure of the shell layer SF changes from random conformation into β-sheet conformation. Because of the increasing of the shell thickness, absorption intensity of X-ray diffraction in the core PBS decreases, but the whole crystallization properties of PBS-SF core-shell ultrafine fibrous membranes does not change significantly.Compared with non-treatment, the tensile strength of the electrospun PBS-SF core-shell composite ultrafine fibrous membranes treated with methanol increases from 14.9 MPa to 17.2 MPa, and the failure strain decreases from 96.8% to 81.8%.