Plasminogen activator inhibitor-1 (PAI-1) is the most important inhibitor of plasminogen activators in plasma and belongs to the serine protease inhibitor (serpin) family. PAI-1 is mainly produced by endothelial cells, smooth muscle cells, and hepatocytes, and is located in the plasma and extracellular matrix. It regulates the fibrinolytic system and thrombus formation by inhibiting tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). PAI-1 plays a crucial role in the development of diseases such as inflammation, tumor invasion, cardiovascular diseases, and metabolic syndrome. Its gene expression is regulated by various physiological and pathological factors, and gene mutations are associated with thrombosis and fibrinolytic disorders.