Objective:To investigate the value of the preoperative peripheral blood lymphocyte-to-monocyte ratio (LMR) in evaluating the prognosis of patients with resectable gastric and esophageal neuroendocrine carcinoma.Methods:The clinical and pathological data of 49 patients with gastric and esophageal neuroendocrine carcinoma in the Third Affiliated Hospital of Soochow University From March 2013 to December 2018 was retrospectively analyzed. The best cut-off value of the preoperative LMR was determined by using the receiver operating characteristic curve (ROC), and patients were divided into low LMR group (LMR<3.587, 24 cases) and high LMR group (LMR&ge;3.587, 25 cases). The clinicopathological characteristics and overall survival (OS) of patients in low and high LMR groups were compared, and the factors affecting the prognosis of patients with gastric and esophageal neuroendocrine carcinoma were explored.Results:The LMR was related to the neutrophil-to-lymphocyte ratio (NLR) ( χ2 = 22.329, P < 0.01) and the prognostic nutritional index (PNI) ( χ2 = 5.384, P = 0.020). The LMR was positively correlated with the PNI ( r = 0.443, P = 0.001) and negatively correlated with the NLR ( r = -0.362, P = 0.011), while the gender, age, tumor maximum diameter, lymph node involvement, T staging, distant metastasis, vascular tumor thrombus, tumor site, treatment method, C-reactive protein-to-albumin ratio (CRP/Alb), and modified Glasgow prognostic score (mGPS) were irrelevant with LMR (all P > 0.05). The median OS time of patients in high and low LMR groups was unreached and 13.1 months (95% CI 5.532-20.735 months), respectively, the low LMR group had a worse prognosis, and the difference was statistically significant ( χ2 = 8.685, P = 0.003). Multivariate analysis showed that the lymph node staging, treatment method and LMR were independent influencing factors of OS (all P < 0.05). Conclusion:Preoperative LMR is a simple and repeatable biological index, which can be considered as an independent influencing factor for the prognosis of patients with gastric and esophageal neuroendocrine carcinoma.