【Abstract】Objective To investigate the effect and mechanism of ectopic viral integration site 1 (EVI1) on the sensitivity of esophageal cancer cells to radiotherapy. Methods 67 tissue samples of esophageal cancer patients received radiotherapy in our hospital were selected. The expression of EVI1 in esophageal cancer tissues was detected by qRT-PCR. Spearman rank correlation analysis was used to analyze the correlation between EVI1 expression and radiotherapy sensitivity. The relationship between EVI1 expression level and clinical pathological parameters of patients were analyzed by statistical analysis. ECA109 cells were routinely cultured, and the radiation-resistant cell line ECA109 (ECA109R) was induced by incremental radiotherapy. MTS was used to detect the 48-hour radiation dose of ECA109 and ECA109R cells for 48 hours. Western blotting was used to detect the expression of EVI1 in ECA109 and ECA109R cells. ECA109R cells were divided into a control group (si-NC group) and an interfering EVI1 expression group (si-EVI1 group) and transfected with siRNA. Western blotting was used to detect the expression of EVI1 in each group of cells, and MTS detected the 48-hour radiation dose of each group cells for 48 hours. After the si-NC group and si-EVI1 group cells were irradiated, the plate clones were used to detect the plate clone formation rate of each group cells, the flow cytometry was used to detect the apoptosis rate of each group cells, and the Western blotting was used to detect the expression of apoptosis-related protein activated caspase 3, Bcl-2 and Bax proteins. Results The expression of EVI1 in esophageal cancer tissues in the radiotherapy-resistant group was higher than that in radiotherapy-sensitive esophageal cancer tissues (P＜0.05). The expression of EVI1 was related to the differentiation and clinical stage of esophageal cancer patients (P＜0.05),EVI1 expression was negatively correlated with radiotherapy sensitivity (P＜0.05). Compared with ECA109 cells, ECA109R cells had an increased IC50 value and EVI1 expression at 48 h (P＜0.05). After siRNA transfection into ECA109R cells, compared with si-NC group, the expression of EVI1 in si-EVI1 group cells decreased and the radiation dose IC50 value decreased (P＜0.05). Compared with the radiation si-NC group, the cell plate clone formation rate of the radiation si-EVI1 group decreased, and the apoptosis rate increased (P＜0.05). Compared with the irradiated si-NC group, the expression of activated caspase 3 and Bax protein in the irradiated si-EVI1 group were increased, and the expression of Bcl-2 proteine was decreased (P＜0.05). Conclusion EVI1 may increase the radiosensitivity of esophageal cancer cells by regulating apoptosis-related proteins and is a potential target for the treatment of esophageal cancer.