Urokinase (UK) [EC 22.214.171.124] is a serine protease that activates plasminogen to plasmin, which in turn degrades fibrin clots. Plasmin has diverse physiological roles apart from its fibrinolytic role in the regulation of blood clotting. It has been implicated in complement activation, cell migration, wound healing, and generation of localized extracellular proteolysis during tissue remodelling, pro-hormone conversion, carcinogenesis and neoplasia. Among the plasminogen activators, UK provides a superior alternative for the simple reasons of its being more potent as compared to tissue-plasminogen activator and nonantigenic by virtue of its human origin unlike streptokinase. Based on these observations, UK is an important anti-thromboembolic drug. Hence, UK, as one of the most potent plasminogen activators is attracting a great deal of attention. In this chapter, we will summarize recent patents related to the occurrence, mechanism of action, structure and function, physico-chemical properties, in vitro production, cloning and expression, purification and applications of UK.