Urokinase-type Plasminogen Activator (uPA) is a serine protease. The primary physiological substrate is plasminogen, which is an inactive form (zymogen) of the serine protease plasmin. Activation of plasmin triggers a proteolysis cascade that, depending on the physiological environment, participates in thrombolysis or extracellular matrix degradation. This links urokinase to vascular diseases and cancer.

Urokinase is used as a thrombolytic agent in research of severe or massive deep venous thrombosis, pulmonary embolism and myocardial infarction.

Urokinase is not very selective for clot-bound plasminogen, unlike tissue plasminogen activator (tPA) which preferentially interacts with clot-bound plasminogen. Because urokinase binds about equally to freely circulating plasminogen and clot-bound plasminogen, it causes significant fibrinogenolysis and clot fibrinolysis making its use less favorable than tPA.