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Metasequoia glyptostroboides Hu et Cheng is the only living species in the genus Metasequoia Miki ex Hu et Cheng (Taxodiaceae),which is well known as a “living fossil” species.In the Chinese folk medicine,the leaves and bark of M.glyptostroboides are used as anti-microbic,analgesic and anti-inflammatory drug for dermatic diseases.This study is the first time to report the free radical scavenging capacity,antioxidant activity and active composition of the bark of M.glyptostroboide.We observed total six extracts and fractions,which were easily obtained by water-ethanol extraction and followed by a further separation with D101 resin column chromatography,had significant DPPH radical,superoxide anion radical and hydroxyl radical scavenging capacity,T-AOC,lipid peroxidation inhibitory activity and metal ions chelating capacity.The fraction MGEB,which was obtained by 60% ethanol extraction and followed by a further separation with D101 resin column chromatograph,possessed the highest proanthocyanidin content and the highest free radical scavenging and antioxidant activities (Fig 1).Furthermore,MGEB could significantly protect against CCl4 induced acute liver injure through inhibition of oxidative stress in mice (Fig 2).Subsequently,this study was carried out to analyze the proanthocyanidin composition of the fraction MGED2 from the bark of M.glyptostroboides.Ten proanthocyanidins including four monomeric flavan-3-ols,catechin (1),epicatechin (2),gallocatechin (3) and epigallocatechin (4),along with six dimeric procyanidins,catechin (4α→8)catechin (5),gallocatechin(4α→8)gallocatechin (6),gallocatechin(4α→8) epigallocatechin (7),gallocatechin(4α→8) catechin (8),catechin(4α→8) gallocatechin (9),gallocatechin(4α→8)epicatechin (10),were isolated (Fig 3).Six of them are reported for the first time from this plant.