Background: Bariatric surgery is a leading treatment for obesity and type 2 diabetes mellitus, with minigastric bypass emerging as a popular option. This study aims to investigate the changes in cellular immunity in patients with postoperative anastomosis after minigastric bypass. Methods: This open prospective clinical study included 152 obese patients who underwent minigastric bypass. Patients were divided into a main group (n=76) with postoperative anastomosis and a comparison group (n=76) without anastomosis. Leukocytes, lymphocytes, and their subpopulations were measured using hematology analyzers, rosette formation, and flow cytometry. Cytokine production (TNF-α, IL-2, IL-10, and IFN-γ) was assessed by sandwich immunoassay and immunofluorescence. Results: In patients with anastomosis, leukocyte counts increased significantly postoperatively, peaking at 13.24x10^9/L on day 3. Lymphocyte counts dropped initially but recovered by day 14. T-helper cells increased progressively, while T-suppressors initially decreased, then doubled by day 14. B-lymphocytes decreased initially but returned to baseline by day 14. In patients with severe anastomosis, proinflammatory cytokine TNF-α production was significantly higher, indicating an intense inflammatory response. Conclusion: Patients with postoperative anastomosis exhibit significant alterations in cellular immunity, characterized by fluctuations in leukocytes, lymphocytes, and increased proinflammatory cytokine production. These findings suggest that immune monitoring is crucial for managing complications after minigastric bypass surgery.