In order to study the effect of mordanting on silk fabrics treated with tannin, those fabrics were treated with Al, Cu, Cr, Fe, Sn by pre and post mordanting. It was studied about color change, weighting effect, dgree of photodegradation by pre and post mordanting. The results are as fallows ; 1. On the addition of mordants into mimosa and tannic acid solution, &{lambda}_{max}& of the former was slightly blue-shifted, on the other hand, &{lambda}_{max}& of the latter was obviously Red-shifted. 2. In case of Cu, Cr, Pre mordanting, weighting effect were appeared. Weighting effect of silk fabrics treated with Tannic acid increased higher than mimosa by mordanting. 3. In color change, Silk fabrics treated with Mimosa and Tannic acid generally changed to red direction and fabrics treated with tannic acid changed to yellow direction by pre and post mordanting. 4. In the photodegradation, the degree of photodegradation on mordanted fabrics increased. Its degree was slack in Cu, Cr, Post mordanting. On the other hand, Al, Fe, Sn were greate. Silk fabrics treated with Mimosa and Tannic acid got inhibiting effect on photodegradation.