Electro-spun silk fibroin (SF) has been studied for biomedical applications because of its good biocompatibility, cyto-compatibility, and simple fabrication method. SF is obtained by a degumming process and the degumming method can affect the degree of molecular degradation of SF during the degumming process. In the present study, the effect of the degumming method on the rheology and electro-spinning performance of a silk solution was examined. In addition, the relationship between the rheology and electrospinnability was investigated. Regardless of the degumming method, all silk formic acid solutions exhibited almost Newtonian fluid behavior. The order of the viscosity of the silk solution was as follows: HTHP method > acid method > soap/soda method. An analysis of the correlation between the viscosity and electrospun morphology showed that the viscosity played a key role in determining the electro-spun morphology, and the critical viscosity for good fiber formation without beads in electro-spinning exists between 0.13 and $0.20Pa{cdot}s$. The viscosity also determines the maximum electro-spinning rate of the SF formic acid solution. The morphology and diameter of the electro-spun fiber were almost unaffected by the electro-spinning rate of the SF solution.