The objective of this study is to compare the spinnability, morphology, structure, mechanical properties, and cell compatibility of the silk fibroin nanofiber nonwoven electrospun fabrics using aqueous (AQ) solution and formic acid (FA) solution. The lower limit concentration was 5 wt% and 3 wt% of AQ solution and FA solution for electrospinning, respectively. The fiber diameter of electrospun fabric using FA solution was larger than that using aqueous solution at the same concentration. The secondary structure contents of silk fabrics were same between AQ and FA solutions. FA was remained in silk nanofibers, and the remained FA could be neutralized. Young's modulus and cell adhesion on electrospun fabric using FA was lower than that using AQ solution. On the contrary, lower cell proliferation rate on electrospun fabric using FA was kept even after neutralization.