Background and Purpose_ Extending the time window is an important strategy in maximizing thrombolytic therapy in stroke patients. ECASS III had examined a 3 to 4.5h time window and showed a benefit to treated patients. However, little is known about safety and efficacy of intravenous recombinant tissue plasminogen activator(rtPA) treatment in the 3 to 4.5 h time window of acute ischemic stroke in chinese people. Methods_ We analyzed data from the Thrombolysis Implementation and Monitor of Acute Ischemic Stroke in China(TIMS-China)- a prospective, multicentric cohort study of intravenous alteplase treatment with patient enrollment from 67 centres across China. Patients who were fully compliant with Chinese product characteristics criteria of alteplase except for the time window and within 4.5 h after symptom onset were included. The symptomatic intracranial hemorrhage, mortality and 90-day outcome of patients treated between 3 and 4.5 h and within 3 h of symptom onset were compared. Results_ A total of 574 patients were included. 165 patients received alteplase between 3 and 4.5 h of symptom onset and 409 patients received altepase within 3 h. In the 3-4.5h cohort, treatment was started at a median of 80 min later after symptom onset (220 min versus 140 min, p<0.0001). After adjustment for the baseline variables including age, sex, past history, aspirin treatment at stroke onset, baseline NIHSS, et al, there were no significant differences between the 3-4.5h cohort and the within 3h cohort for any outcome measure-rate of symptomatic intracranial haemorrhage(2.42% versus 1.47%, p=0.70); mortality(5.70% versus 6.33%, p=0.52); and independence(70.25% versus 64.56%, p=0.15). Conclusion_ Our study suggests that intravenous rtPA treatment also remains safe and effective for chinese people between 3 and 4.5 h of symptom onset after acute ischemic stroke.