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Background: Vine tea from fermented Ampelopsis grossedentata leaves has been used as a herbal tea and folk medicine in the southern region of China for hundreds of years. The aim of this investigation was to analyze the total flavonoids found in vine tea, including three bioactive flavonoids, and the total phenolic contents in the aqueous methanol extracts of 10 vine tea samples. In addition, this study also aimed to examine the antioxidant activity of dihydromyricetin and vine tea's flavonoid-rich extract. Methods:The total flavonoids and total phenolic content assay of extracts from vine tea were performed by ultraviolet-visible spectroscopy and epoch microplate spectrophotometer, respectively. Three bioactive flavonoids were quantified simultaneously using high performance liquid chromatography. The antioxidant activity of dihydromyricetin and vine tea's flavonoid-rich extract was evaluated in vitro using six different methods. Results: Vine tea contained a large number of flavonoids, with dihydromyricetin as its main constituent. The flavonoid-rich extract exhibited a significant scavenging effect on superoxide anion radicals, and on 3-ethylbenzthiazoline-6-sulphonic acid and 1,1-diphenyl-2-picrylhydrazyl radicals. It also possessed definite activity in lipid peroxidation inhibition, ferric reduction, and the moderation of Fe2+ ion chelation ability. There was a significant negative correlation between dihydromyricetin content and antioxidant activity in the vine tea samples, including superoxide anion radical scavenging activity (P = -0.754, P < 0.05), lipid peroxidation inhibition activity (P = -0.759, P < 0.05), ferric-reducing antioxidant power (P=-0.843, P<0.01), respectively. Dihydromyricetin played a dominant role in the antioxidant activities of the flavonoid-rich extract. Conclusion: Vine tea's flavonoid-rich extract could be used as a new antioxidant source to safeguard against oxidative stress.