Abstract: Ultrasonic-assisted extraction of flavonoids from Euonymus japonicus and their antioxidant activities were first investigated in this study.The optimum extraction condition for flavonoids was established by single-factor and orthogonal experiment.The optimal extraction conditions for flavonoids were as follows: solid to liquid ratio for 1∶30 ( g/mL) , 80% ethanol concentration, ultrasonic extraction for 60min and extraction twice. And this optimal extraction condition of orthogonal experiment was verified, the average flavonoids extraction yield was 3.82%.Also, scavenging activities of the flavonoids on hydroxyl, superoxide anion and reducing power were determined, the results showed that compared with positive control VC, flavonoids from Euonymus japonicus excelled in scavenging activity on hydroxyl radical, whereas it had weaker activity on scavenging superoxide anion radical as well as the reducing power. These results clearly indicated that flavonoids from Euonymus japonicus were effective in scavenging free radicals and had the potential to be antioxidants and also provided the theoretical data for supporting the use of Euonymus japonicus as medicinal plant.