HGF activator (HGFA) is a serum-derived serine protease and belongs to the peptidase family S1.HGFA is responsible for the conversion of hepatocyte growth factor (HGF), from the inactive single-chain precursor to the active heterodimeric form, which is a potent mitogen, motogen, and morphogen for liver cells, epithelial cells, and endothelial cells. HGFA is synthesized and secreted by the liver and circulates in the plasma as an inactive single-chain zymogen in normal states. The zymogen is cleaved by thrombin or thermolysin through the endoproteolytic process and forms an active heterodimer linked by a disulfide bond. In turn, the active protease can be inhibited by HGFA inhibitors (HAIs) including HAI-1 and HAI-2. In addition, the HGFA zymogen acquires a strong affinity upon activation and thus may ensure the local action in tissue regeneration in liver, kidney and skin. It has been reported that activation of HGF is a critical limiting step in the HGF/SF-induced signaling pathway mediated by Met, and accordingly, aberrant expression of HGFA is implicated in tumorigenesis and progression.