A case of primary chylopericardium in a 54 year-old-man was reported. Despite 3 times of pericardiocentesis, the pericardial fluid accumulated rapidly. After the fenestration of pericardium, a small cannula was inserted for the thoracic ductgram which showed a clearly visible duct upward to the angulus venosus and an abnormal branch near the bifurcation of the trachea spilling some contrast material into the pericardial cavity. Ligation and division of the thoracic duct including an abnormal branch was performed from its entry to the thorax for a length of 13 cm upward. The postoperative course was uneventful and chest X-ray film taken 6 months after surgery showed no accumulation of chyle in the pericardium and pleural cavity.