Effect of reducing agent sodium hydrosulfite on the natural indigo on the silk fabrics were examined to improve traditional dyeing method. K/S values of dyed fabrics was monitored with various dyeing temperature time, amount of dye and reducing agent. The dyeability of silk fabrics was improved by using reducing agent, sodium hydrosulfite; K/S value (7.20) was higher then that (1.09) of traditional method at the frist dyeing. Natural indigo dye extracted from dyed silk fabrics are composed of isomer, indigo (67.3%) and indirubin (32.5%). However, silk fabrics showed excellent anti-microbial activity regardless of the dyeing methods.