〔Abstract〕 Objective To analyze the levels of interleukin 6(IL-6) in different groups of patients with severe fever with thrombocytopenia syndrome(SFTS) and to investigate the clinical predictive value of IL-6 levels oon the severity and prognosis of the disease. Methods According to the severity and prognosis, 105 patients with confirmed SFTS were divided into mild group VS severe group and improved severe group VS the poor prognosis group.The difference between IL-6 and each clinical indicator in different groups was compared and the correlation between IL-6 and various indexes was analyzed.Multivariate Logistic regression was used to analyze the independent risk factors of the severity and prognosis, and receiver operating characteristic curve(ROC) was used to assess the predictive value of IL-6 for severity and prognosis in SFTS patients. Results The lymphocyte number(L),platelet number(PLT) and albumin(ALB) were lower in the severe group than those in the mild group, and the age, IL-6,aspartate aminotransferase(AST),creatine kinase isoenzyme(CKMB),lactate dehydrogenase(LDH),mitochondrial aspartic transaminase(mAST),blood amylase(AMY),lipase(LPS),α-hydroxybutyrate dehydrogenase(HBDH) and calcitonin(PCT) were higher in the severe group(allP<0.05); age, IL-6,HBDH,LPS and PCT were higher in the poor prognosis group than those in the mild group(allP<0.05),while the differences in other indicators were not statistically significant(allP>0.05). Levels of IL-6 were associated with AST,creatine kinase(CK),CKMB,LDH,HBDH,mAST AMY,LPS and PCT were positively correlated(allP<0.05),and negatively correlated with L,monocyte count(M),PLT and ALB(allP<0.05),while there was no significant correlation with other indexes.IL-6 was found to be an independent predictor of severity and prognosis in the multifactorial logistic regression analysis.When predicting severe disease, the area under the curve(AUC) was 0.883,with a sensitivity and specificity of 61.54% and 98.04%,respectively; when predicting poor prognosis, the AUC was 0.937,with a sensitivity and specificity of 88.00% and 88.89%,respectively. Conclusion IL-6 level has an important clinical value in evaluating the severity and prognosis of SFTS patients.