Objective: To study the antioxidant activity of different fractions and chemical constituents from Semiaquilegiae Radix in vitro. Method: Different extraction fractions from Semiaquilegiae Radix were ethyl acetate extraction(TK-Y)

n-butanol extraction(TK-Z)

water extraction(TK-S) and polysaccharide(TK-D). Under the chemical simulation conditions in vitro

the antioxidant activities of different extraction fractions and polysaccharide were determined by · OH

O2- · scavenging experiments. Furthermore

the chemical compounds were isolated from bio-active fraction. Result: The antioxidant activities of different extraction fractions from strong to weak were as follows:TK-D>TK-S>TK-Z>TK-Y.Scavenging activity of TK-D for O2- · and · OH were positively correlated (Y=54.94X+27.15

R2=0.998 3)

IC50=0.42 g · L-1.Five major components were isolated and identified from TK-Z as lithtospermoside(1)

thalictricoside(2)

griffonilide (3)

β-sitosterol(4)

daucosterol(5). Conclusion: The polysaccharide

n-butanol extraction and water extraction are active fractions and it identified the active fractions of Semiaquilegiae Radix for the first time. Lithtospermoside

thalictricoside and griffonilide were found as main contribution.