Serpina9, also known as serpin A9, is a member of the Serpin superfamily of serine protease inhibitors. Serpins are the most broadly distributed superfamily of protease inhibitors that use a conformational change to inhibit target enzymes. They are known to inhibit serine proteases and some are known to inhibit caspases and papain-like cysteine proteases. Serpins are conformational labile and many of the disease-linked mutations of serpins result in misfolding or in pathogenic, inactive polymers. This protein shows inhibition towards trypsin, thrombin, and plasmin and binds DNA and heparin. Recombinant mouse Serpina9, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.