Abstract: Objective: To explore the clinical significance of serum miRNA-206 expression in differentiating bacterial infections and severity of infections by detecting serum miRNA expression profiles in Pseudomonas aeruginosa(PA) pneumonia and healthy individuals. Methods: Ninety-five patients with PA pneumonia infection and 90 healthy individuals were recruited for this study.The differentially expressed miRNAs between the two groups were confirmed by quantitative PCR.Receiver operating characteristic(ROC) curve and logistic regression analyses were performed to assess the ability of altered serum miRNAs to differentiate between patients with PA and healthy individuals as well as patients with different levels of infection. Results: Relative expressions of miR-206 were significantly higher in serum of patients with pneumonia than those in healthy individuals.Area under the ROC curve was 0.768 (95%CI:0.699-0.863,P<0.01).When the optimal cut-off value was 0.51,the sensitivity and specificity of miR-206 for the diagnosis of PA were 57.70% and 88.50%,respectively.Logistic regression analysis showed that miR-206 levels predicted the severity of PA infections (mild vs severe OR=0.545,95%CI:0.362-0.823,P<0.01;moderate vs severe OR=0.774,95%CI:0.639-0.936,P<0.01). Conclusions: Serum miR-206 can be used as a serological marker for identification,diagnosis and assessment of severity of PA induced pneumonia.