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AIM: Antioxidant activity is one of the important indexes for estimating medicinal value for the traditional Chinese medicine. The aim of this study is to investigate the antioxidant activity of 11 flavonoids mainly revealing luteolin as mother nucleus isolated from Pyrethrum tatsienense. MATERIALS AND METHODS: The antioxidant activity of 11 flavonoids was measured in vitro using the classical 1,1-diphenyl-2-picrylhydrazyl removal method. The percentages of scavenging activity of 11 flavonoids were analyzed by taking the choice of a-tocopherol as positive drugs, and the scavenging activity was plotted against the sample concentration to obtain the IC50 values. RESULTS: Ten flavonoids containing phenolic hydroxyl groups have different levels of antioxidant activity. Antioxidant activity mainly depends on the numbers and the substitutional positions of phenolic hydroxyls in B ring. When C-3', 4' positions in B ring of flavonoids are replaced by hydroxyl groups, the antioxidant activity improved remarkably. Phenolic hydroxyl groups in A ring contribute some to antioxidant activity because of the electrophilic effect of C ring, and the numbers and substitutional positions of methoxyl and glycosyl have a little effect on the antioxidant activity. CONCLUSION: Structure-activity relationships of antioxidant activity about flavonoids isolated from P. tatsienense are concluded, which will be beneficial to deep understanding the pharmacological functions of this Tibetan medicine in vivo from the point of antioxidation.