Background: Recently, several nutritional and inflammatory markers have been reported to be involved in cancer progression. The aim of this study is to evaluate whether nutritional and inflammatory biomarkers such as the modified Glasgow prognostic score (mGPS), the neutrophil‐to-lymphocyte ratio (NLR), the platelet‐to-lymphocyte ratio, the systemic-immune-inflammation index (SIII), controlling nutritional status (CONUT) score, prognostic nutritional index, and the lymphocyte‐to-monocyte ratio (LMR) could predict the prognosis in patients with unresectable pancreatic ductal adenocarcinoma (UR-PDAC) who underwent chemotherapy as first-line therapy, using disease-specific survival as the primary outcome. Methods: All UR-PDAC patients were retrospectively evaluated between January 2011 and May 2017 at Toyama University Hospital. Baseline clinicopathological characteristics and pre-treatment laboratory values such as absolute neutrophil, lymphocyte and platelet counts, C-reactive protein, albumin and CA19-9 levels, were collected. Results: A total of 184 patients were diagnosed as UR-PDAC. Among them, 151 patients who underwent chemotherapy were enrolled in this study. There were significant relationships between survival and elevated mGPS, elevated NLR, elevated SIII, decreased LMR, decreased serum cholinesterase level, and low CONUT score (p < 0.001, p < 0.001, p = 0.001, p < 0.001, p = 0.026 and p < 0.001, respectively, by log-rank test). The median survival time of patients with metastatic lesions was significantly shorter than that of patients with unresectable locally advanced PDAC (9.0 vs 15.5 months, respectively; p = 0.033). There was no significant difference in survival in pre-treatment CA19-9 level and tumor location. Multivariate analysis using Cox regression model revealed that NLR and CONUT score were independent prognostic factors. Conclusions: Pre-treatment NLR and CONUT score may predict clinical outcome in patients with UR-PDAC undergoing chemotherapy as first-line therapy.