Objective To investigate the prognostic value of serum high mobility group box-B1 (HMGB1) in the patients with sepsis. Methods A total of 342 patients with sepsis who were admitted to Renji Hospital (South Campus) Shanghai Jiao Tong University School of Medicine, from January 2018 to December 2021 were enrolled. There were 192 male and 150 female sepsis patients, with an average age of (60.54±17.85) years. The patients were divided into the survival group and the death group based on 28-day outcome. The clinical data were collected and the level of HMGB1 on admission was tested. COX multivariate regression was used to analyze the risk factors for poor prognosis of the sepsis patients. Pearson correlation analysis was performed to analyze the correlation between serum HMGB1, sequential organ failure assessment (SOFA) and acute physiology and chronic health evaluation Ⅱ(APACHEⅡ) score. Receiver operator characteristic (ROC) curves were drawn to analyze the area under the ROC curve (AUC) and cut-off value of serum HMGB1 to evaluate the prognosis of sepsis. According to the cut-off value of serum HMGB1, the patients were divided into high level group and low level group. Kaplan Meier survival curve was drawn to further analyze the relationship between serum HMGB1 and prognosis. Results The mortality rate of sepsis patients was 29.2% (n=100). The indexes which included the level of serum HMGB1, C-reactive protein, procalcitonin, white blood cell count, lactic acid level, SOFA and APACHEⅡ score, the proportion of respiratory tract infection, septic shock, disseminated intravascular coagulation and mechanical ventilation in sepsis death group were significantly higher than those in survival group (all P<0.05), while the proportion of diabetes mellitus and urinary tract infection were significantly lower than those in survival group (all P<0.05). Multiple regression analysis showed that serum HMGB1 level, SOFA score, white blood cell count and respiratory tract infection were the risk factors for 28-day mortality. Pearson correlation analysis presented that serum HMGB1 level was positively correlated with SOFA score and APACHEⅡ score in the sepsis patients (P<0.001). The ROC curve showed that AUC of HMGB1, SOFA score and APACHEⅡ score for predicting 28-day mortality were 0.776, 0.774 and 0.760, respectively. Kaplan Meier survival curve found that 28-day mortality was significantly higher in the patients with higher HMGB1 levels than those with lower HMGB1 levels (P<0.001). Conclusions Serum HMGB1 level increased significantly in the death group, which was one of the risk factors for predicting 28-day mortality, and its predictive efficacy was not inferior to SOFA and APACHEⅡ score.