The natural dyeing of silk fabric with natural gardenia blue powder was investigated. The sum of K/S values was increased with increasing the amount of gardenia powder up to 20%,(o.w.b.). The proper time, temperature and pH for the dyeing of silk fabric with gardenia blue powder were 60~80 minutes, $80^{circ}C$ and pH 4, respectively. The B and BG colors were obtained according to various mordanting methods, mordants and mordant concentrations. The various colorfastness were not improved by mordanting. The colorfastness to light was poor, but the colorfastness to dry cleaning and washing were good.