Thrombin, also named factor IIa (FIIa), is a serine protease present in the coagulation cascade. Thrombin activates factor XI, VIII, V, XIII and fibrinogen.

Our α-thrombin is a resultant of bovine plasma prothrombin, activated by FXa with the aid of FVa and phospholipid, and purified by ion exchange chromotography and gel filter chromotography.

It is mainly used in anti-FIIa activity assay of heparin.