Abstract: The objective of this study was to optimize the extraction process of flavonoids from Abrus precatorius Linn, and explored its antioxidant activity. Ethanol volume fraction, solid-liquid ratio, ultrasonic energy and ultrasonic extracting time as variables, the yield of flavonoids as evaluation index, single factor tests and Box-Behnken method were used to optimize the extraction process. The scavenging ability on DPPH, ABTS⁺ free radicals, and the reducing power of flavonoids from Abrus precatorius Linn were also detected to estimate the antioxidant activities. When solid-liquid ratio reaches 1:50, the results showed that optimum extraction process (0.696%, highest yield) can be achieved under condition of ethanol volume fraction 82%, ultrasonic Energy 507 J and ultrasonic extracting time 42 min. Half effective concentration being EC₅₀ 0.028 mg/mL and 0.009 mg/mL respectively. Abrus precatorius Linn flavonoids were able to scavenge DPPH and ABTS⁺ free radicals effectively, and its ability risen as mass concentration increases, meaning it is superior to Trolox. When flavonoid concentration was set at 5 mg/mL, the reducing power on iron ion reached 2.42 mmol/L, which was weaker than Trolox but prior to some plant flavonoids. To sum up, ultrasonic extraction technology can be effectively employed to the extraction of Abrus precatorius Linn flavonoids, resulting in better antioxidant activity.