To investigate natural dyeing properties of bast fiber, properties of pre mordanting dyeing of sappan wood, gardenia and gallnut such as K/S values, developed color, and fastness were evaluated. Silk showed the most increased K/S values by pre mordanting treatment when Fe was uses as a mordant. The optimized amount of Fe was 3%. The colors of sappan wood was a series of YR. After pre mordanting treatment with Fe, the colors of bast fiber of mulberry and silk showed a series of RP, and the color of cotton showed a series of Y. The color of gallnut was a series of Y regardless of pre mordant treatment. Sappon wood (YR), gardenia (Y), and gallnut (Y) showed various colors such as YR, R, and RP, respectively. Sunlight fastness was not improved by pre mordanting treatment. The effect of pre mordanting treatment was not good. Especially the treatment with Al showed poor sunlight fastness.