Serpin B9 gene encodes a member of the serine protease inhibitor family which are also known as serpins. The encoded protein belongs to a subfamily of intracellular serpins. This protein inhibits the activity of the effector molecule granzyme B. Overexpression of this protein may prevent cytotoxic T-lymphocytes from eliminating certain tumor cells. A pseudogene of SerpinB9 gene is found on chromosome 6. Serpin B9 is a protein that in humans is encoded by the SERPINB9 gene. PI9 belongs to the large superfamily of serine proteinase inhibitors (serpins), which bind to and inactivate serine proteinases. These interactions are involved in many cellular processes, including coagulation, fibrinolysis, complement fixation, matrix remodeling, and apoptosis.