BackgroundThe effects of body mass index (BMI) on mortality of sepsis remain unknown, since previous meta-analyses have reported conflicting results. Several observational studies published recently have provided new evidence. Thus, we performed this updated meta-analysis.MethodsPubMed, Embase, Web of Science, and Cochran Library were searched for articles published before February 10, 2023. Observational studies that assessed the association of BMIs with mortality of sepsis patients aged > 18 years were selected. We excluded studies of which data were unavailable for quantitative synthesis. Odds ratios (OR) with 95% confidence interval (CI) were the effect measure, which were combined using fixed-effect or random-effect models. The Newcastle–Ottawa Scale was applied for quality assessment. Subgroups analyses were conducted according to potential confounders.ResultsFifteen studies (105,159 patients) were included in the overall analysis, which indicated that overweight and obese BMIs were associated with lower mortality (OR: 0.79, 95% CI 0.70–0.88 and OR: 0.74, 95% CI 0.67–0.82, respectively). The association was not significant in patients aged ≤ 50 years (OR: 0.89, 95% CI 0.68–1.14 and OR: 0.77, 95% CI 0.50–1.18, respectively). In addition, the relationship between morbidly obesity and mortality was not significant (OR: 0.91, 95% CI 0.62–1.32).ConclusionsOverweight and obese BMIs (25.0–39.9 kg/m2) are associated with reduced mortality of patients with sepsis or septic shock, although such survival advantage was not found in all crowds.Trial registrationThe protocol of this study was registered in PROSPERO (registration number CRD42023399559).Supplementary InformationThe online version contains supplementary material available at 10.1186/s40560-023-00677-0.