Abstract: Objective To investigate the prognostic value of the systemic immune-inflammation index（SII） in pancreatic ductal adenocarcinoma（PDAC） after neoadjuvant chemotherapy. Methods The clinical data of PDAC patients who received pancreatectomy in Panjin Liao Oil Baoshihua Hospital from January 2013 to December 2016 were analyzed retrospectively. SII was detected after neoadjuvant chemotherapy. The ROC curve was used to determine the optimal cutoff value of SII，by which the patients were divided into SII>885 group（n=37） and SII ≤885 group（n=58）. Cox regression was used to evaluate the relationship between SII and postoperative survival of PDAC patients. Results SII was related to tumor size，biliary drainage，and CA19-9 levels before surgery（P<0.05）. The 3-year survival rate of the SII≤885 group was higher than the SII >885 group（43.1% vs 18.9%，P=0.015）. Multivariable Cox regression showed that intraoperative tumor size>3 cm（HR=1.367，95%CI：1.227-2.215，P=0.031），CA19-9>37 IU/mL（HR=1.292，95%CI：1.132-1.931，P=0.011），SII＞885（HR=1.451，95%CI：1.327-2.431，P=0.021） were independent risk factors of postoperative survival of PDAC patients. Conclusion SII＞885 suggests poor prognosis in patients with PDAC after neoadjuvant chemotherapy.

Key words: Pancreatic ductal adenocarcinoma, Systemic immune-inflammation index, Neoadjuvant chemotherapy, Prognosis