To evaluate the clinical efficacy and safety of piperacillin/ tazobactam in the treatment of hospital acquired pneumonia( HAP) . Methods A multicenter, open-labeled, non-comparative clinical trial was conducted. Patients with HAP were administered intravenously with piperacillin /tazobactam( 4. 5 g) every 8 h for 7-14 days. Results A total of 250 patients were enrolled in this study and 246 subjects were clinical valuable. At the end point, the clinical efficacy rate was 81. 7% ( 201 /246) and the bacterial eradication rate was 74. 1% ( 83 /112) . The rate of drug related adverse events was 2. 8% ( 7 /250) , in which 4 cases had clinical significance ( rash, dyspnea, injection site pain and diarrhea, respectively) and 3 cases had abnormal laboratory findings ( hepatic dysfuction , eosinophilia and so on ) . All events were mild and transient . Conclusions Piperacillin/ tazobactamis effective and safe in the treatment of HAP, therefore, it is recommended as one of the first-line antibiotics to treat the patients with HAP.