Objective To longitudinally investigate the characteristics of postoperative weight changes in patients with esophageal cancer and analyze its influencing factors, which can provide certain guidance for nutritional intervention in patients with esophageal cancer. Methods Patients with esophageal cancer who underwent surgical treatment at the Sichuan Cancer Hospital from December 2020 to February 2022 were prospectively included. The general information questionnaire and body composition analyzer were used to longitudinally investigate the patients’ weight and body composition before surgery (T0), 1 month after surgery (T1), 3 months after surgery (T2) and 6 months after surgery (T3), and the change characteristics were analyzed. The generalized estimating equation was used to analyze the influencing factors for postoperative weight changes in patients with esophageal cancer. Results A total of 130 patients were enrolled, including 110 males and 20 females, aged 42-79 (63.33±8.16) years. The weight and body composition of patients with esophageal cancer showed a continuous slow downward trend within 6 months after surgery. The weight loss rate of patients at 1, 3, and 6 months after surgery was 5.10%, 7.76%, and 9.86%, respectively. The analysis results of the influencing factors for postoperative weight showed that patients with the following characteristics had more weight loss: female (β=−7.703, P=0.001), ≥60 years (β=−3.657, P=0.010), smoking (β=4.622, P=0.010), low tumor differentiation degree (β=4.314, P=0.039), and high frequency of eating (β=−3.400, P=0.008). Conclusion Weight loss is an important health problem for patients with esophageal cancer after surgery, and patients have a continuous downward trend in weight within 6 months after surgery. Medical staff should pay special attention to the patients who are female, ≥60 years, having smoking history and low tumor differentiation degree.