AIM to evaluate the association of body mass index(b MI) with the overall survival of pancreatic ductal adenocarcinoma(PDAC) patients.METHODS A retrospective analysis of PDAC patients diagnosed in the National Cancer Center of China between January 1999 and December 2014 was performed. these patients were categorized into four b MI groups(< 18.5, 18.5-22.9, 23-27.4 and ≥ 27.5 kg/m2). χ2 tests for comparison of the proportions of categorical variables, and Student’s t-test or Mann-Whitney test for continuous variables were employed. Survival analysis was performed with the Kaplan-Meyer method. their HRs of mortality and 95%CIs were estimated using the Cox proportional hazards model.RESULTS With a median age of 59.6 years(range: 22.5-84.6 years), in total 1783 PDAC patients were enrolled in this study. their mean usual b MI was 24.19 ± 3.53 for the whole cohort. More than half of the patients(59.3%) experienced weight loss during the disease onset and progression. Compared with healthy-weight individuals, newly diagnosed patients who were overweight or obese had more severe weight loss during their disease onset and progression(P < 0.001). Individuals who were overweight or obese were associated with positive smoking history(P < 0.001). A significant difference in comorbidity of diabetes(P = 0.044) and coronary artery disease(P < 0.001) was identified between high b MI and normal-weight patients. After a median follow-up of 8 mo, the survival analysis showed no association between b MI and the overall survival(P = 0.90, n = 1783). When we stratified the whole cohort by pancreatic cancer stage, no statistically significant association between b MI and overall survival was found for resectable(P = 0.99, n = 217), unresectable locally advanced(P = 0.90, n = 316) and metastatic patients(P = 0.88, n = 1250), respectively. the results did not change when we used the b MI at diagnosis.CONCLUSION Our results showed no significance of b MI for the overall survival of PDAC patients.