Choledochal cyst, or cystic dilatation of the common bile duct, is generally considered to be an uncommon indiopathic congenital condition that may produce symptoms in infancy but more of ten is discovered at some time during the first two decades of life. Female patients have outnumbered males 3 or 5 to1, and almost cases reported by many authors had more than two symptoms among the classic triad of abdominal mass, jaundice and upper abdominal pain. Authors would like to submit here with the brief review of the literature and report on 2 cases of idiopathic dilatation of the common bile duct that they had experiences among the Pediatric inpatient at Busan St. Benedict Hospital, and the diagnosis was established by clinical, laboratory, X-ray and surgical findings. Cases I in 14 year old girl was complained of severe abdominal distension, jaundice, pruritus and abdominal mass. On 7th admission day, exploratory laparatomy was done and choledochal cyst of 1722cm in size was confirmed and has been followed up for 1 year after Roux-en-Y choledochojejunsotomy without any complications. Cases II in 9 year old boy was complained of intermittent fever, jaundice, colicky abdominal pain and upper abdominal mass. On 6th admission day, exploratory laparatomy was done and choledochal cyst of 1015cm in size was confirmed and has been followed up for 1 year after choledochoduodenostomy with cholecystectomy without any complications.