Abstract: Concerning the quality of valonia tannin, there are two different views. This paper attempts to find out a solution of this problem. A review of the possible pathway of the biosynthesis of valonia tannin and the seven individual tannins, with different structures, in the valonia extract was made. Experiments were carried out for the evaluation of valonia tannin. The effect of aping on the change of tan solution showed that the tannin/nontannin ratio was decreased as the aging time prolonged, which indicated that the chemical behaivor of the complex components of the tan liquor was unstable. They are going to change continuously with aging and during the tanning process but will always keep a relative balance between tannin and nontannin. The rate of diffusion of valonia tannin was quick. It's tanning power to combine with collagen was strong. Leather tanned with fresh valonia extraet was of good quality, plumpness, solidity, high weight yield and the physico-chemical properties agreed with the sole leather quality index. Therefore it is sugested that valonia tannin is one kind of the best tannins.