Abstract: The indirubin was extracted from natural indigos by using ultrasonic-assisted ethyl acetate.With the same concentration of ascorbic acid and Vc as the control，the antioxidant activity of indirubin was investigated by testing scavenging effects of ·OH and against the peroxidation of oils.The results showed that the extraction ratio of indirubin reached 0.12% under the following conditions:ethyl acetate as extraction agent,1∶10 (g/mL) of material-liquid-ratio,40 w ultrasonic power,13 kHz ultrasonic frequency and 250 W heating power within 50 min.Indirubin extract exhibited ability to remove ·OH and good inhibitory effect on peroxidation of oils.The antioxidant activity was increased with concentration of indirubin increasing,and the activity was better than those of ascorbic acid and Vc.

Key words: ultrasonic, ethyl acetate, indigo naturalis；indirubin；antioxidant activity