Serpins are the largest and most diverse family of serine protease inhibitors which are involved in a number of fundamental biological processes such as blood coagulation, complement activation, fibrinolysis, angiogenesis, inflammation and tumor suppression and are expressed in a cell-specific manner. Most serpins are secreted and attain physiologic concentrations in the blood and extracellular fluids. Mouse SerpinB12 is a cytoplasm protein which belongs to the serpin family and Ov-serpin subfamily. It is expressed in many tissues, including brain, bone marrow, lymph node, heart, lung, liver, pancreas, testis, ovary, and intestine. SerpinB12 inhibits trypsin and plasmin, but not thrombin, coagulation factor Xa, or urokinase-type plasminogen activator.