Abstract: An ultrasonic-assisted aqueous two phase extraction method was presented for extracting total flavonoids from Porphyra yezoensis and the extraction conditions were optimized by an orthogonal array experimental design. Meanwhile, the hydroxyl free radical scavenging activity of total flavonoids from Porphyra yezoensis was determined. The results indicated that the method allowed effective extraction of total flavonoids. The extraction yield was 0.148%, which was significantly higher than that obtained by ethanol-water reflux extraction. The optimal extraction conditions were obtained as follows: n-propanol-to-water ratio 0.6, ammonium sulphate concentration 0.30 g/mL, ultrasonic treatment time 20 min and material-to-liquid ratio 0.04. P. yezoensis abundantly contained flavonoids and the total flavonoid extract from it had excellent hydroxyl free radical scavenging activity thus providing a good natural free radical scavenger.

Key words: ultrasonic-assisted aqueous two-phase extraction, Porphyra yezoensis, flavonoids, antioxidant activity