OBJECTIVE: To investigate the diagnostic and prognostic value of miR-9-5p in peripheral blood mononuclear cells in sepsis patients. METHODS: Differentially expressed miR-9-5p in sepsis were screened from a database and available literature. Subsequently, iBMDM cell validation was conducted and the expression level of miR-9-5p in peripheral blood mononuclear cells was determined using RT-qPCR in 69 sepsis patients and 30 non-sepsis patients with infections, 24 hours after ICU admission. A control group that comprised 35 healthy individuals, matched for age and sex, was set up from those who agreed to provide blood samples laboratory analysis. RESULTS: On admission to the ICU, the levels of miR-9-5p were significantly higher in sepsis patients (10.13 [3.21, 24.94]) than in non-sepsis patients with infections (2.08 [1.68, 3.18]) and healthy controls (0.86 [0.36, 1.88]) (p < 0.001). The miR-9-5p levels were positively correlated with the severity of the disease as indicated by the SOFA score (r=0.656, P<0.001). The AUC of miR-9-5p in predicting sepsis, septic shock, and in-hospital death was 0.825, 0.821, and 0.845, respectively. CONCLUSION: Elevated expression levels of miR-9-5p in peripheral blood mononuclear cells are significantly associated with an increased risk of sepsis and septic shock, and also indicate a higher risk of organ dysfunction.