Natural indigo dyeing has been used mainly on cellulosic fibers and silk during the course of history in Korea. In order to extend the usage of this one of the most important natural dyes, its dyeability on wool fabrics has been studied to find out the optimum dyeing condition for wool fiber which is susceptible to alkaline medium. The dyeing method used was hydrosulphite vat of extracted dye. K/S values of dyed fabrics were investigated to analyze the dyeability of natural indigo on wool fibers and colors were measured through $L^*,;a^*,;b^*$ and Munsell Values. Highest K/S values were obtained at the temperature of 60(C and pH 7 to 8. The Munsell Values for hue of wool fabrics dyed with extracted indigo powder using hydrosulphite vat fell mostly in PB range. As the dyebath pH increased, blueness increased. Different dyeing conditions resulted in change of colors of dyed fabrics due to the difference in amounts of indigotin and indirubin contents within the dyed fiber as shown by HPLC.