Background: An accurate assessment of the severity and prognosis of sepsis, especially septic shock, is vital for the tailored treatment of this condition. miRNA participates in the inflammatory response and cell apoptosis and regulates inflammation-related signaling pathways. Immune disorders often accompany sepsis. Since serum miRNA expression is superior to traditional biological markers in terms of sensitivity and specificity, its role in the assessment of sepsis has increasingly been recognized. Methods: Serum miRNAs were extracted from septic patients and healthy individuals by using the ultracentrifugation method. The differential expressions of miRNAs in the serum samples were detected by high-throughput sequencing technology. The differentially expressed miRNAs between the two groups were analyzed by bioinformatics. The quantitative polymerase chain reaction real-time polymerase chain reaction (qRT-PCR) was used to amplify the sample size to verify the results and to screen the highly-expressed miR-206 in septic patients. Subsequently, serum samples were collected from 63 septic patients, and 30 patients with septic shock and qRT-PCR were performed to analyze the expression of miR-206. These 93 patients were divided into the miR-206 low-expression group and miR-206 high-expression group according to miR-206 expression level. The potential correlations between the miR-206 expression and the clinical data were analyzed by using SPSS 25.0. Results: Serum miRNA expression significantly differed between septic patients and healthy individuals.High-throughput sequencing results showed that, compared with those in healthy individuals, 29 miRNA molecules were down-regulated, and 25 molecules were up-regulated in the serum samples of septic patients. qRT-PCR identified the significantly up-regulated miR-206 in septic patients. qRT-PCR also showed significantly higher miR-206 expression levels in patients with septic shock than in septic patients. Furthermore, we observed a significantly longer prothrombin time and activated partial thromboplastin time, and significantly higher SOFA score, APACHE-II score, and in-hospital mortality rate. miR-206 was positively correlated with SOFA sore and APACHE-II score.Conclusions: Serum miR-206 expression is positively correlated with the severity and prognosis of sepsis.Thus, it may be a potential biomarker for assessing the severity and prognosis of sepsis, although the specific mechanism warrants further investigations.