Objective: Neoadjuvant therapy followed by surgery has been the standard treatment for advanced esophageal cancer. Severe toxicities may influence body composition, including skeletal muscle mass, and increase postoperative complications. The purpose of this study was to evaluate the influence of sarcopenia, changes in body composition, and adverse events during neoadjuvant chemotherapy (NACT) on postoperative complications in esophageal cancer patients. Methods: A total of 83 patients with esophageal cancer undergoing NACT followed by esophagectomy were included. Body composition was assessed before chemotherapy and before esophagectomy. The relationships between postoperative infectious complications and sarcopenia, changes in body composition, and adverse events during NACT were investigated. Results: Univariate analysis revealed that skeletal muscle loss during NACT, but not preoperative sarcopenia, was significantly higher in the complication (+) group. Febrile neutropenia tended to occur frequently in the complication (+) group. Multivariate analysis demonstrated that skeletal muscle loss was the only factor significantly associated with infectious complications (p = 0.029). Among adverse events, febrile neutropenia was significantly associated with a decrease in skeletal muscle mass. Conclusion: Loss of skeletal muscle mass during NACT was a significant risk factor for postoperative infectious complications in patients with esophageal cancer. Prevention of severe adverse events may reduce postoperative infectious complications.