The objectives of this study are to evaluate the efficacy and safety of gentamicin usage based on plasma concentrations in No.108 Central Military Hospital. Methods: This is a prospective observational study included twenty seven adult patients admitted to the Tubeculosis and Pulmonary Disease Department and Neurology Department of No.108 Military Central Hospital from April to June 2009. The patients were treated with gentamicin, and blood samples were taken to determine Cpeak and Ctrough at steady state. The evaluation of the efficacy was based on Cpeaks and the safety was based on Ctroughs. Results: The rates of patients that had not achieved Cpeak and Ctrough in the recommended ranges were 40.8 percent and 37 percent respectively. Conclusions: The results suggested that the usage of gentamicin not be really effective and safe, maybe due to interindividual variability of pharmacokinetic parameters. Therapeutic drug monitoring of gentamicin, therefore, should be applied regularly. Further studies to identify the varies of pharmacokinetic parameters of the patients in a larger number will provide valuable information for TDM in these patients.