Abstract: An ultrasound-assisted process to extract flavonoids from the fruits of Ligustrum obtusifolium was optimized, and the antioxidant activity of the extract analyzed in vivo. Based on a single factor test on ethanol concentration, solvent:substrate ratio, and ultrasonic application duration, the extraction procedure was optimized using response surface methodology based on flavonoid yield as the indicator. With an in vivo feeding, the level of malondialdehyde (MDA) and activity of superoxide dismutase (SOD) in livers of the test mice were determined. The optimal processing conditions, including a solvent:substrate ratio of 11 mL:1 g, an ultrasonic application for 11 min, and the use of 60% ethanol for solvent, rendered a flavonoid yield of (4.83±0.03)mg·g^-1 for the extraction. The extract obtained significantly suppressed MDA production and raised SOD activity in livers of the mice.