Abstract Background: One cause of anastomotic leakage after radical esophagectomy is blood flow insufficiency at the cervical anastomosis site. Therefore, evaluation of blood flow in the gastric tube is important in preventing anastomotic leakage. In this study, we focused on the repeated measurement of tissue oxygen saturation (rSO2) before and after raising the gastric tube to the cervical area and also at the actual anastomotic site in the gastric tube. Methods: Eighteen patients were studied. rSO2 was measured at the tip (point pre 0) and 2, 4, and 6 cm on the distal side of the tip (point pre 1, pre 2, and pre 3) before the gastric tube was raised to the cervical site through the retrosternal route. After that, rSO2 was measured at the tip, 2 and 4 cm on the distal side of the tip (points post 0, post 1, and post 2), the actual anastomotic site (point AN). The relationship between rSO2 scores and the rate of anastomotic leakage was determined. Results: The mean rSO2 at pre 0, pre 1, pre 2, and pre 3 were 48.9%, 52.3%, 54.8%, and 56.9%, respectively (p < 0.05). The mean rSO2 at post 0, post 1, and post 2 were 47.8%, 50.5%, and 52.3%, respectively, and the rSO2 at point AN was 52.1%. Anastomotic leakage was found in 6 patients. The rSO2 at points pre 0, pre 1, and pre 2, post 0 and point AN were significantly lower in patients with anastomosis leakage than those without it (p < 0.05). Conclusion: Tissue oxygen saturation monitoring was a useful indicator of blood flow insufficiency in the gastric tube during radical esophagectomy.