Silk Fibroin (SF) nanofibers containing various silver compounds, such as silver tetrafluoroborate, silver phosphate, silver sulfadiazine, and silver acetate, were prepared by electrospinning. Silver compounds were dissolved into SF solution in 98% formic acid. In this system, the formic acid was used both as a co-solvent of SF and silver compounds, and as a reducing agent for silver ions in solution. The average diameters of SF nanofibers varied depending on the type of silver compounds added. The Ag element in the SF nanofibers was confirmed to be mainly Ag nanoparticles by XPS results. The in vitro cytotoxicity of silver compounds in SF nanofibers on normal human keratinocytes and fibroblasts was examined. Overall, the silver compounds in SF nanofibers are cytotoxic to both normal human epidermal keratinocytes (NHEK) and normal human epidermal fibroblasts (NHEF) cells.