Objective:To systematically evaluate the effects of body mass index (BMI) on the prognosis of patients with diffuse large B-cell lymphoma (DLBCL).Methods:The databases (PubMed, Medline,Web of Science) were searched to identify clinical literatures about the relationship between BMI and the prognosis of DLBCL according to the inclusion and exclusion criteria. RevMan 5.3 software was used to analyze hazard ratio ( HR) and 95% confidence interval (95% CI) of overall survival (OS) and progression-free survival (PFS); the quality of included literatures, publication bias risk and heterogeneity were also evaluated. Results:There were 12 articles included in our research. Meta-analysis result showed that compared with normal weight patients (BMI 18.5-24.9 kg/m 2), the overweight patients (BMI 25.0-29.9 kg/m 2) had longer OS and PFS time, while the differences were not statistically significant (OS: HR=0.93, 95% CI 0.78-1.11, P=0.42; PFS: HR=0.89, 95% CI 0.67-1.20, P=0.45). The under-weight (BMI < 18.5 kg/m 2) (OS: HR=1.97, 95% CI 1.41-2.74, P < 0.01; PFS: HR=1.89, 95% CI 1.19-3.03, P < 0.01) and the obesity (BMI≥30.0 kg/m 2) patients both had shorter OS and PFS time, but the latter had no statistically significant difference (OS: HR=1.15, 95% CI 0.88-1.51, P=0.31; PFS: HR=1.32, 95% CI 0.90-1.94, P=0.15). No publication bias was observed in the symmetric funnel plot analysis. Conclusion:The increased BMI within a certain range is a protective factor for the prognosis of DLBCL patients.