We investigated the optimal treatment for refractory chylothorax after pediatric cardiovascular surgery. We retrospectively reviewed the cases of 15 consecutive patients who developed chylothorax after congenital heart surgery performed between December 2004 and November 2010. Among the 15 patients (12 male and 3 female; median age 13.9 months) who developed postoperative chylothorax, 10 recovered with conservative therapy, such as a low-fat diet, medium chain triglyceride–enriched diet, or total parenteral nutrition. Of the remaining 5 patients who underwent surgical treatment followed by conventional therapy, 4 showed improvement, and 1 died from cardiac failure. Surgical treatment was performed at a median of 19 days after diagnosis of chylothorax. Average drainage output of thoracocentesis for the first 5 days before thoracic duct ligation was 33.1 ml/kg/day. Duration of chylous fluid drainage was significantly longer in surgical patients than in patients who recovered with conservative therapy (p < 0.01). Surgical patients tended to be younger with lower body weight. Significant risk factors for surgical intervention were age <4 months, body weight <4 kg, and duration of drainage >10 days. In cases of refractory postoperative chylothorax, surgical therapy such as thoracic duct ligation should be considered when discharge from the drainage tube is >30 ml/kg/day or chylothorax is not improved within 10 days.