Abstract: Objective: The aim of this study is to evaluate the thrombolytic effects of nattokinase (NK) produced by Bacillus subtilis natto LNUB236 in vitro and in vivo. Methods: The thrombolytic effect of NK in vitro was determined by the dissolution rate of blood clots. Meanwhile, the in vivo effect was assessed by using a carrageenan-induced rat tail thrombosis model and a ferric chloride-induced carotid arterial thrombosis model as well as measuring mouse tail bleeding time. The toxicity of NK was measured by acute toxicity test (14 days) and chronic toxicity test (28 and 90 days) in rats. Results: NK significantly increased the dissolution rate of blood clots, while it significantly reduced the length of carrageenan-induced rat tail thrombus and the mass of ferric chloride-induced-carotid thrombus (P < 0.05). In addition, NK significantly prolonged the tail bleeding time of mice. In the acute and chronic toxicity tests, the tissues of the mice in the NK group had no pathological damage, and blood biochemical indexes were in the normal range. Conclusion: The NK produced by Bacillus subtilis natto LNUB236 exerts a thrombolytic activity both in vitro and in vivo, without any toxicity for the body. This study can lay the foundation for the development of functional foods containing NK produced by Bacillus subtilis natto LNUB236.

Key words: nattokinase, thrombolytic activity, toxicity