Electrospinning is a good method to obtain nanoscale fibers from polymer solutions. In this paper, we successfully prepared non-woven nanofibers of Bombyx mori and Samia cynthia ricini silk fibroins, and of the recombinant hybrid fiber involving the crystalline domain of B. mori silk and non-crystalline domain of S. c. ricini silk from hexafluoroacetone (HFA) solution using electrospinning method. C-13 cross polarization/magic angle spinning NMR spectroscopy was used to monitor the structural change of silk fibroins together with the detection of the residual HFA during the process of the fiber formation. Scanning electronic microscope was used to determine the diameters and their distributions of the fibers.