Abstract: An ultrasonic extraction of flavonoids from Mucunae sempervirens was optimized using a single factor response surface methodology. The content, hydroxyl radical scavenging capacity and bovine serum albumin (BSA) combining ability of the resulting extract were determined for the evaluation. The results showed the optimized conditions to include a methanol volume fraction of 60% and a solid-liquid ratio of 1:25 (g·mL^-1) with 420 W ultrasound applied for 20 min to reach a total extracted flavonoid content of 3.64 mg·g^-1. In comparison to the verification content of 3.58 mg·g^-1, the difference between the theoretical and experimental values was 1.64% indicating that a reasonable and feasible result had been reached. The hydroxyl radical scavenging rate of the extract was 85.35%, and the fluorescence quenching effect of the extract on the BSA combination test followed the exponential function of Y=-233.9 ln(X) + 25.665 (R²=0.9906).