Objective To explore the optimal diameter for the first dilation of mild to moderate benign stenosis of the anastomotic site after radical resection of esophageal malignant tumors. Methods A retrospective analysis was conducted on the clinical data of 83 patients with benign anastomotic stenosis after radical resection of esophageal malignant tumors from January 2015 to June 2022. According to the diameter of the first endoscopic balloon dilation, they were divided into 12mm, 13.5mm, and 16mm groups. The safety, effectiveness, and prognosis of the three treatment groups were compared.Results The success rates of expansion in the three groups were 81.0%, 90.9%, and 92.5%, respectively, and the incidence of complications was 4.8%, 4.5%, and 5.0%, respectively, with no statistically significant difference (P=0.369; P=0.999). The 12 month restenosis rates were 94.1%, 95.0%, and 67.6%, respectively. Compared with the 12mm and 13.5mm groups, the 16mm group had a significant decrease in the 12 month restenosis rate (P=0.034, P=0.019). The median recurrence time of stenosis in the 12mm group was 2 (1.00, 3.00) months, the median recurrence time of stenosis in the 13.5mm group was 3.5 (1.00, 5.25) months, and the median recurrence time of stenosis in the 16mm group was 6.5 (1.50, 12.00) months. The recurrence time of stenosis in the 16mm group was significantly shorter than that in the 12mm and 13.5mm groups (P=0.026, P=0.048), and the median number of redilations in the three groups after dilation was 3 (2.00, 4.00), 2 (1.75, 3.25), and 2 (0.00, 2.00) times, respectively. The expansion frequency of the 16mm group was significantly reduced compared to the 12mm and 13.5mm groups (P=0.003, P=0.032)However, there was no significant difference between the 12mm group and the 13.5mm group (P>0.05). A diameter of<5mm before dilation, a diameter of<15mm after initial dilation, and a distance of ≥ 3 months from initial dilation to surgery are risk factors for restenosis within one year after dilation (OR>1, P<0.05).Conclusion For mild to moderate benign stenosis of the anastomotic site after radical resection of esophageal malignant tumors, the optimal diameter for initial endoscopic dilation is 16mm