Nattokinase (EC 3.4.21.62) is a serine protease and profibrinolytic enzyme with a strong fibrin-degrading activity, and many host strains can produce it. By its comparison with other fibrinolytic enzymes such as (streprokinase, urokinase and t-PA), nattokinase showed many advantages of having long life-time, no side effects, costless and it owns the ability to be a drug candidate for treatment of heart diseases and used as an effective food additive. Bacillus subtilis natto discovered in natto, a typical Japanese fermented soybean food. After the purification of Nattokinase from the supernatant of B. subtilis culture media, it showed a strong fibrinolytic activity. The enzyme was refined to a 4.4-fold purity level, with 61.8 percent of activity recovered. SDS-PAGE showed that nattokinase is homogenous and identified it as a monomer of 29000 Da in its original state. The optimum temperature and pH were 65°c and 9.0 respectively. Purified nattokinase is thermally stable at temperatures ranging from 35 to 55 °C and alkaline stable at pH 7.0 to 10.0. Skim milk agar showed clear zone of crude enzyme. Mg²⁺ increased the activity of nattokinase, but Zn²⁺ and Fe³⁺ decreased the activity. Triton x-100 as detergent significantly increased activity of nattokinase on the contrast to SDS inhibit nattokinase activity.