Objective:To study the predictive value of the systemic immune inflammation index (SII) on the overall survival rate of patients after Whipple surgery for pancreatic ductal adenocarcinoma (PDAC).Methods:The clinical data of patients with PDAC who underwent Whipple surgery at the First Affiliated Hospital of Zhengzhou University from January 1, 2010 to December 31, 2017 were retrospectively analyzed, and the SII value was calculated. The best cut-off value of SII was 900, and all patients were divided into the low SII group (SII≤900) and the high SII group (SII>900) using 900 as the dividing point. The Kaplan-Meier method was used to draw survival curves and the log-rank test was used. The overall survival of the two groups of patients were analyzed. The Cox risk regression model was used to perform univariate analysis of the various clinicopathological parameters, and multivariate analysis for the statistically significant indicators.Results:Of 135 patients enrolled into this study, there were 78 males and 57 females, aged 28.0-76.0 (56.6±8.8) years. There were 92 patients in the low SII group, aged (56.9±9.2) years with 53 males and 39 females; and 43 patients in the high SII group, aged (56.1±7.9) years, with 25 males and 18 females. The median survival of the low SII group and the high SII group were 32.7 months (95% CI: 28.4-37.0) and 24.4 months (95% CI: 21.4-27.4), respectively. The survival of patients with PDAC in the low SII group was significantly higher than that in the high SII group ( P<0.05). On univariate survival analysis, postoperative overall survival of patients with PDAC was significantly associated with high SII ( HR=2.047, 95% CI: 1.354-3.096), R 1 margin ( HR=2.595, 95% CI: 1.663-4.048), a positive rate of lymph node>20% ( HR=3.244, 95% CI: 1.888-5.573), and positive regional lymph node (N1) ( HR=3.061, 95% CI: 1.993-4.702), all P<0.05. Multivariate Cox regression analysis showed that high SII ( HR=1.672, 95% CI: 1.094-2.555), R 1 resection margin ( HR=2.167, 95% CI: 1.274-3.685), and a positive rate of lymph node>20% ( HR=2.631, 95% CI: 1.309-5.285) to be independent risk factors affecting overall survival ( P<0.05). Conclusion:SII was an independent prognostic factor available before surgery for patients with PDAC. It has some guiding significance in predicting overall survival in patients after Whipple surgery for PDAC.