Nattokinase (pronounced nat-oh-KY-nase) is an enzyme (EC extracted and purified from a Japanese food called nattō. Nattō is made from fermented soybeans and has been eaten in Japan for about a thousand years. Nattō is produced by fermentation by adding the bacterium Bacillus natto to boiled soybeans. Nattokinase is produced by the bacterium acting on the soybeans. While other soy foods contain enzymes, it is only the nattō preparation that contains the specific nattokinase enzyme.

In spite of its name, nattokinase is not a kinase enzyme, but a serine protease of the subtilisin family. It exhibits a strong fibrinolytic activity.[2][3] Nattokinase can now be produced by recombinant means[4][5] and in batch culture,[6][7]rather than relying on extraction from Nattō.

There are three well-known manufacturers around the world, including Contek Life Science Co., Ltd, Daiwa Pharmaceutical Co., Ltd and Japanese Nattokinase Association organized by Japan Bio Science Laboratory Co., Ltd.