Objective：To analyze the association of cellular and humoral immunity indices with the severity of disease and prognosis in patients with sepsis. Methods：A total of 71 patients with sepsis included in the study were divided into sepsis group（37 cases） and septic shock group（34 cases） according to the severity of disease，and into survival group（58 cases） and death group（13 cases） according to the 28-day outcome. The Acute Physiology and Chronic Health Evaluation Ⅱ（APACHE Ⅱ） score and the Sequential Organ Failure Assessment（SOFA） score were determined when the patients were admitted to the ICU，and their immunological in－dices were measured. The differences in the above indices between the sepsis group and the septic shock group were statistically ana－lyzed. The receiver operating characteristic（ROC） curve was used to analyze the clinical value of the above indicators in evaluating the prognosis of the patients. Results：Compared with the sepsis group，the septic shock group had significantly higher APACHE Ⅱ score，SOFA score，CD4+/CD8+，and complement 4（C4） level（P<0.05），but significantly lower T lymphocyte percentage and comple－ment 3（C3） level（P<0.05）. Compared with the survival group，the death group had significantly higher APACHE Ⅱ score and SOFA score（P<0.05），but significantly lower CD4+/CD8+ and C3 level（P<0.05）. A multivariate logistic regression analysis suggested that SOFA score and C3 level were predictors of the severity of sepsis. According to the results of ROC curve analysis，the ar－eas under the ROC curve for CD4+/CD8+，APACHE Ⅱ score，and SOFA score were 0.807，0.843，and 0.853，respectively（P<0.05）；in predicting sepsis-induced death，CD4+/CD8+ had a sensitivity of 69.2% and a specificity 86.2% at the optimal cut-off value of 21.9%，APACHEⅡ score had a sensitivity of 76.9% and a specificity of 79.3% at the optimal cut-off value of 22，and SOFA score had a sensitivity of 76.9% and a specificity of 79.3% at the optimal cut-off value of 17.5. Conclusion：T lymphocyte percentage，CD4+/CD8+，C3，and C4 are associated with the severity of sepsis，which provides a potential value in assess－ing the severity of sepsis. C3 is an independent predictor of the severity of sepsis. CD4+/CD8+ can reflect the prognosis of patients with sepsis.