Abstract: Objective: To explore the optimal ultrasonic extraction processing and antioxidant activity of total flavonoids from Cirsium japonicum. Methods: The total flavonoids in Cirsium japonicum were extracted by ultrasound-assisted alcohol extraction method and the content of total flavonoids was determined by UV spectrophotometry. The antioxidant activity of total flavonoids from Cirsium japonicum was evaluated by the scavenging capability for superoxide anion and hydroxyl free radicals. Results: The optimal extraction conditions for total flavonoids from Cirsium japonicum were ethanol concentration of 75%; material/liquid ratio of 1:30 and ultrasonic treatment time of 45 min. Under the optimal extraction conditions, the extraction rate of total flavonoids was 0.289%. The total flavonoids from Cirsium japonicum exhibited an obvious scavenging effect on free radicals. The antioxidant activity of total flavonoids was a dose-dependent in the certain concentration range.

Key words: spectrophotometry, Cirsium japonicum, ultrasonic extraction, total flavonoids, antioxidant