Persimmon tannin was extracted from persimmon pulp with methanol acidified with 1% HCl, then AB-8 macroporous adhesive resin and polysulfone ultrafilter membrane with molecular weight cutoff of 10000 were employed to purify and fractionate the crude extract, and two fractions: Small Molecular Weight Tannin(SMWT) and High Molecular Weight Tannin(HMWT) were obtained. The molecular weight distribution of HMWT was determined to be in the range of 1.16×10⁴ to 1.54×10⁴. Antioxidant properties of HMWT were evaluated in 2-deoxy-D-Ribose system, methyl violet system, salicylic acid system, pyrogallol autoxidation system, and linoleic acid lipid peroxidation system. The maximum scavenging rate of HMWT on hydroxyl radical in 2-deoxy-D-Ribose, methyl violet and salicylic acid system were 90.47%, 96.46% and 87.77%, respectively; the maximum inhibiting effect of HMWT on pyrogallol autoxidation and linoleic acid lipid preoxidation were 56.57% and 69.63%, respectively. HMWT exhibited excellent antioxidant activity in all tested sytems in a dose-dependent manner and the antioxidant activity of HMWT was significantly stronger than those of SMWT and grape seeds proanthocyanidins(OPC). This results suggest that HMWT is the main antioxidant in persimmon pulp.