Abstract: Objective: To extract the protein fraction with fibrinolytic activity from Sipunculus nudus Linnaeus and evaluate the antioxidant activity.Methods: Fresh Sipunculus nudus were precipitated with PBS buffer( 0.02 mol/L,p H7.5) to homogenize and the clear supernatant of tissue homogenate was salting out with stepwise ammonium sulfate to obtain the protein fraction with highly fibrinolytic enzyme activity.The antioxidant activity was investigated by using methods of purssian blue reaction,DPPH,phenanthroline and pyrogallol autoxidation. Result: The protein fraction with highly fibrinolytic enzyme activity was obtained by using 30% saturation ammonium sulfate to remove the mixed protein,and then by 50% saturated ammonium sulfate to obtain the target protein precipitation. The protein fraction had reduction ability and strong scavenging effect on DPPH· and ·OH.The concentration of scavenging 50%( EC₅₀) of DPPH· and ·OH were 1.23 mg /m L and 6.07 mg /m L respectively. Whereas it had significant negative scavenging ability on O₂^-·.Conclusion: The protein fraction with fibrinolytic activity from Sipunculus nudus Linnaeus obtained by two steps ammonium sulfate salting out method had certain antioxidant capacity.