Recombinant human prourokinase (rhPro-UK) is a novel thrombolytic that has been approved to treat patients with acute myocardial infarction. However, the safety and efficacy of intravenous rhPro-UK in patients with acute ischemic stroke (AIS) has not been well established. We aimed to investigate the safety and preliminary efficacy of rhPro-UK in patients with AIS in a multi-center phase Ha trial setting. One hundred nineteen patients within 4.5 h of AIS onset were enrolled in this randomized, open-label, 23-center phase Ha clinical trial. Patients were randomly assigned to 35 mg (n = 40) or 50 mg (n = 39) intravenous rhPro-UK or 0.9 mg/kg recombinant tissue plasminogen activator (r-tPA; n = 40). The primary endpoint was functional independence defined as a modified Rankin scale (mRS) score of 0 or 1 at 90 days. The secondary outcome was early neurological improvement defined as a reduction of >= 4 points on the National Institutes of Health Stroke Scale (NIHSS) score from baseline to 24 h after drug administration. Safety endpoints included death due to any cause, symptomatic intracerebral hemorrhage (sICH), and other serious adverse events (SAEs). The proportion of patients with an mRS score of <= 1 at 90 days did not differ significantly among three groups (35 mg rhPro-UK: 55.56% vs. 50 mg rhPro-UK: 57.89% vs. vs. r-tPA: 52.63%; P = 0.92). The rates of treatment response, referring to early neurological improvement, were similar among these three groups (36.11% vs. 31.58% vs. 28.95%, respectively; P=0.85). There was no difference in mortality at 90 days or in the rate of other SAEs among the three groups. One patient in the 50 mg rhPro-UK group suffered sICH. While neither the primary efficacy outcomes nor safety profile differed significantly among the low, high rhPro-UK and control groups, it is a logical step to further test the low-dose rhPro-UK group versus the control group in a well-powered phase III study.