Abstract: In this study,total flavonoids were extracted from the abandoned branches of Toona Sinensis by ultrasound-assisted extraction method and their antioxidant activities were assessed by potassium ferricyanide reduction,salicylic acid colorimetric method and 1,1-diphenyl-2-picrylhydrazyl( DPPH) radical scavenging assays.Temperature,liquid-to-solid ratio and ultrasonic power were identified by single factor method as main variables that affect the extraction yield of total flavonoids. The levels of the three variables were optimized by response surface methodology.The results showed that the optimal conditions for ultrasound-assisted extraction of total flavonoids were found to be 59 ℃,a liquid-to-solid ratio of 51 m L/g and ultrasonic power of 174 W.Under the optimized conditions,the extraction yield of total flavonoids was 7.94%. The antioxidant assays showed that the extracted flavonoids presented a strong antioxidant activity to scavenge·OH and DPPH radicals with IC50 values of0.205 mg/m L and 0.018 mg/m L,respectively.These values were both lower than the IC50 values of ascorbic acid of1.022 mg/m L and 0.069 mg/m L,respectively. Ultrasound-assisted extraction not only produced high yield of flavonoids,but also greatly shortened processing time,which provided a reference for developing new processes of total flavonoids from the abandoned branches of Toona Sinensis.