The studies were performed to investigate the optimum conditions for tannic processing of silk by use of Chinese Gallotannin and synthesized tannic acid, which are aimed at weighting, dyeing and physical properties of tannin treated silk. 1. It was reasonable that the concentration of tannin solution is 30 grams per liter of Chinese Gallotannin, 13 grams per liter of tannic acid for the efficient weighting of processed silk. The temperature and time for tannin treatment was optimum at 80°C, 60 minutes and the acidity of tannin solution at pH 2 to 3. 2. In dyeing the tannin treated silk by Acid dye Orange II , the temperature and time was reasonable at 60°C, 90 minutes to control the desorption of tannin components weighted onto silk. 3. The colour differences (ΔE) of dyed silk fabric by soaping could be remarkably narrowed by tannin treatment, resulting in improving the washing fastness of tannin treated silk by two grades more than that of untreated one. 4. The light fastness of tannin treated silk could be drastically improved by reducing the dye-loss of dyed silk fabric which was coused from the Ultra-violet ray irradiation. 5. The rubbing fastness and water repellency of tannin treated silk was at the same level with that of untreated one. However, the Drape coefficient of tannin treated silk was decreased more than that of untreated one, which is closely related with fabric softness and dressing appearence.