Abstract: Objective:Observed effect of nattokinase on the tail-thrombus model, and provided basis for the function evaluation of nattokinase product.Methods:The mice were randomly allocated into four groups (each group with 12 mice) , including the normal group, the model control group, the low-dose nattokinase group, and the high-dose nattokinase group.Weighing up the mice was done every 7d.After the mice were fed for 30d, except for the normal group, other 3 groups were used to establish tail-thrombus models with carrageenan.After models were established for 24h, we observed the length of dark tails, and then detected the Fibrinogen degradation product (FDP) , tissue type plasminogen activator (t-PA) , and tissue type plasminogen activator inhibitor (PAI-1) in serum.Results:There was no significant difference between the length of dark tails among the model control group, the low-dose nattokinase group and the high-dose nattokinase group (p>0.05) , but the dark tail rates of the later two group were lower than the former one.The values of FDP and t-PA of the high-dose nattokinase group were higher than those of the model control group and the low-dose nattokinase group (p<0.05) .no PAI-1 was detected in the normal, and other groups had similar values of PAI-1.Conclusions:Nattokinase was effective in dissolving blood clots, and dropping incidence of disease.Carrageenan induced tail-thrombus model could be used to evaluate the antithrombotic and fibrinolysis enhancing effects of nattokinase.