Chylothorax is the most common cause of pleural effusion in the neonatal period and is defined as an effusion of lymph in the pleural cavity. We report a case of chylothorax in 8-day-old male who was admitted due to respiratory difficulty. Chest AP roentgenogram showed pleural effusion of the left lung, and milky yellow fluid was aspirated via thoracentesis. Diagnosis was confirmed by chemistry studies of pleural lipid and lipoprotein electrophoresis. Chyle obtained from pleural space was diagnosed by their high triglyceride levels and the finding of chylomicrons on lipid electrophoresis. He was treated by thoracentesis, chest tube insertion, feeding with formulas containing medium-chain triglyceride and total parenteral nutrition without oral feeding. He was discharged on the 45th hospital day in good health.