Intravenous thrombolysis is the first-line therapy in patients with acute ischemic stroke within 4·5 hours of symptom onset, and recombinant tissue plasminogen activator (alteplase) is the preferred thrombolytic agent for this purpose. RhPro-UK is a specific plasminogen activator. rhPro-UK only acts on occlusive thrombus and has little effect on hemostatic thrombus. In addition, rhPro-UK does not form covalent complexes with protease inhibitors in plasma, so the concentrations of rhpro-UK and protease inhibitors in the blood do not decrease compared with alteplase. Therefore, rhPro-UK therapies have a potential advantage of less systemic bleeding in treated subjects. Data from several previous studies suggest that rhPro-UK is efficacious when used to treat patients with acute myocardial infarction. On April 2, 2011, rhPro-UK injection was approved by the National Medical Products Administration to treat acute myocardial infarction. Since then, rhPro-UK has been widely used to treat myocardial infarction in China. Since 2016, a phase 2 clinical trial was carried to explore the dosing of rhPro-UK in patients with acute ischemic stroke, followed by another study with a sample size of 680 patients to initially validate the efficacy and safety of the proposed dose of 35mg. The results of these studies suggested that rhPro-UK was effective, and there were no safety concerns. To further prove the efficacy and safety of rhPro-UK in patients with acute ischemic stroke, investigators conducted this phase 3 study (PROST-2).