This study were carried out to investigate the effects of mordants and mordanting methods under the various dyeing conditions such as temperature, time, pH, repetition of dyeing in the silk fabrics with Petasites japonicus leaf. It was the most high K/S values of the silk fabrics dyed with Petasites japonicus leaf according to co mordanting and used cupric sulfate, ferric sulfate as mordanting agents. K/S values of the silk fabrics dyed with Petasites japonicus leaf were increased gradually with dyeing temperature, dyeing time, repetition of dyeing was higher and the optimum pH was pH 7. Silk fabrics were colored yellowish orange and surface color(munsell value) was changed from 8.3YR to 2.0Y by using mordanting agents and those of the silk showed high tone when mordanting with cupric sulfate but decolored and darked when mordanting with ferric sulfate. Washing fastness of silk fabrics were good in 4 ～ 5 grade, so washing fastness of the silk fabrics was significantly improved when washed with the neutral detergent.