Inflammation-based prognostic indicators have been developed to predict the prognosis in patients with pancreatic cancer. However, prognostic indices have not been established in patients with unresectable pancreatic cancer, including those without indication for chemotherapy at diagnosis. This study aimed to identify the predictors in all patients with unresectable pancreatic cancer. We retrospectively analyzed data of 119 patients with unresectable pancreatic cancer from June 2006 to September 2018. The following laboratory parameters were evaluated: the Glasgow Prognostic Score (GPS), modified GPS, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), C-reactive protein albumin (CRP/Alb) ratio, and prognostic nutritional index (PNI). We performed time-dependent receiver operating characteristic analysis, overall survival (OS) analysis, and univariate and multivariate analyses to determine the prognostic factors in patients with unresectable pancreatic cancer. The cut-off value for NLR was determined to be 3.74. The 6-month OS rates in low and high NLR groups were 75.5% and 18.8% (P < 0.001). In the univariate analysis, advanced age (P = 0.003), metastatic pancreatic cancer (P = 0.037), no treatment (P < 0.001), worse Eastern Cooperative Oncology Group Performance Status (ECOG-PS) (P < 0.001), high GPS (P < 0.001), high modified GPS (P < 0.001), high NLR (P < 0.001), high PLR (P = 0.002), high CRP/Alb ratio (P < 0.001), and low PNI (P < 0.001) were identified as the prognostic factors. The multivariate analysis revealed that metastatic pancreatic cancer (P = 0.046), no treatment (P < 0.001), worse ECOG-PS (P = 0.002), and high NLR (P < 0.001) were independently associated with OS. We revealed that the high NLR could be an independent indicator of poor prognosis in patients with unresectable pancreatic cancer.