BACKGROUND: Chylothorax is a postoperative complication in patients with lung cancer. Diet-control approaches have been the mainstay for managing this condition. However, a surgical intervention is needed for the patients if conservative treatment is ineffective. Because of the lack of accurate indicators to assess the prognosis of the postoperative complication at an early stage, the criteria of surgical treatment were not consistent. METHODS: We reviewed 2942 patients who underwent pulmonary resection and lymph node dissection for primary lung cancer at our hospital between March 2021 and December 2022. The prognostic implications of clinical indicators were assessed in patients with postoperative chylothorax who were managed with a low-fat diet. Binary logistic regression was used to explore the predictive value of these indicators for patient prognosis. RESULTS: Postoperative chylothorax occurred in 108 patients and 79 patients were treated with a low-fat diet management while 29 patients were managed with TPN. In contrast to drainage volume, the pleural effusion triglyceride level after 2 days of low-fat diet exhibited enhanced predictive efficacy in predicting patient prognosis. When the pleural fluid triglyceride level of 1.33 mmol/L was used as the diagnostic threshold for prognosis, the sensitivity and specificity reached 100% and 80.6%, respectively. CONCLUSIONS: The pleural effusion triglyceride level after 2 days of low-fat diet can serve as a valuable prognostic indicator in patients undergoing lung surgery and experiencing chylothorax. This predictive approach will help thoracic surgeons to identify patients with poor prognosis in a timely manner and make decision to perform necessary surgical interventions.