The purpose of this study was to retrospectively investigate the prognostic significance of the lymphocyte-to-monocyte ratio (LMR) in patients with middle and advanced thoracic malignant tumors (esophageal and lung cancer) prior to and after radiotherapy. The clinical data of 74 patients with middle-advanced stage lung and esophageal cancer who received radiotherapy in Jiangsu Shengze hospital from January 2017 to December 2021 were screened for this retrospective analysis. Peripheral blood was collected, and LMR was recorded before and within one week following radiotherapy. The receiver operating characteristic curve (ROC) was established to obtain the best cut-off value for overall survival (OS). The correlation between LMR and prognosis before and after radiotherapy was examined. The Kaplan-Meier method was used to create the survival curve, and Cox proportional hazard regression model was used for univariate and multivariate analysis. The median follow-up time was 15 months, and the median age was 70 years. According to the ROC curve, the best critical value of LMR prior to radiotherapy was 2.46, AUC=0.719, while the best critical value of LMR after radiotherapy was 1.07, AUC=0.682. The Cox risk ratio model showed that clinical stage, diagnosis, combination therapy, and LMR before and after radiotherapy were all related to prognosis. Multivariate analysis revealed that clinical stage, combination therapy, and LMR before and after radiotherapy were independent prognostic factors in patients with middle and advanced lung and esophageal cancer following radiotherapy (p<0.05). LMR before and after radiotherapy was associated with the prognosis of patients with middle and advanced thoracic tumors. Patients who accepted radiotherapy for middle and advanced lung and esophageal cancer with high LMR had a better prognosis.