Considering lower body weight in Chinese population, a lower dose of 50mg rt-PA/2h may exhibit similar efficacy and safety as 100mg/2-h rt-PA for treating acute PTE in this population. We, therefore, compared these two regimens in a multi-center, randomized, controlled trial. The efficacy was assessed by the improvement of the right ventricular function on echocardiograms, perfusion defect score of lung V/Q scans or quantitative computed tomographic (CT) evaluation, safety was evaluated by incidence of major or minor bleeding, death rate, and PTE recurrence on 24h,14d after treatment.