Abstract:This study aims to improve the purity of flavonoids in the ethanol-water extract of mulberry leaves.To be specific，the ethanol-inorganic salt aqueous two-phase extraction system was used to separate and purify the crude mulberry flavonoid extract（MFE）.The extraction conditions were optimized by single factor test and Box-Behnken design.The antioxidant activity of mulberry leaf flavonoids 1 and 2 （MLF1，MLF2）was evaluated based on the scavenging rates of·OH，ABTS+·，DPPH·and O2-·，and the variation of the activity after the extraction was detected.The results showed that the optimal conditions for the ethanol-inorganic salt aqueous two-phase extraction were ethanol of 36%，ammonium sulfate of 17%，and MFE of 5 mg/mL.Under the above conditions，the extraction achieved two-phase volume ratio R=1.84 ± 0.17，partition coefficient K=11.82±0.34，and extraction rate Y=（95.74±0.58）%.As for the in vitro antioxidant activity，the·OH，ABTS+·and DPPH·scavenging rates of MLF2 were higher than those of rutin，but the O2-·scavenging rate was lower than that of rutin.Moreover，the various antioxidant indexes of MLF2 were higher than those of MLF1.Therefore，the ethanol-inorganic salt aqueous two-phase extraction system was applicable to the extraction of flavonoids from mulberry leaves，as it enhanced the antioxidant activity of them.