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. Results showed that, when solid-liquid ratio reached 1:50, the optimum extraction process (0.696%, highest yield) could 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 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. To sum up, ultrasonic extraction technology can be effectively employed to the extraction of Abrus precatorius Linn flavonoids, resulting in better antioxidant activity.