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The edible flowers of Caragana sinica are used in China a kind of health-promoting vegetable. In this study, the antioxidant activities of its ethanol extract, as well as its petroleum ether, ethyl acetate, n-butanol and water fractions, were evaluated through in vitro model systems including the DPPH, FRAP and β-carotene bleaching methods. Among the C. sinica flower extracts the ethyl acetate fraction was the most effective. Correlation analysis suggested that flavonoids might be the major contributors to the high antioxidant activity of this flower. Six flavonoids including quercetin (1), isoquercitrin (2), rutin (3), quercetin-3′-O-methyl-3-O-α-L-rhamnopyranosyl (1→6)-β-D-glucopyranoside (4), typhaneoside (5) and quercetin-3-O-β-D-glucopyranosyl(1→2)[α-L-rhamnopyranosyl (1→6)]-β-D-glucopyranoside (6), were isolated from this flower for the first time. Their contents were determined by a HPLC method. Compounds 3 and 4 were found to be the major flavonoids, with concentrations of 1.20 ± 0.07 and 3.94 ± 0.12 mg/g dry sample, respectively. These results demonstrated that the C. sinica flowers may be valuable natural antioxidant sources and are potentially applicable in the health food industry.