Herein, we report a case of chylothorax following total thymectomy. A 46-year-old woman having an anterior mediastinal tumor underwent a thymectomy via median sternotomy. Seven days after surgery, there was no massive pleural effusion. However, on post-operative day 17, a right massive pleural effusion was detected, and it was diagnosed as chylothorax. She was successfully treated with conservative therapy. Chylothorax following thymectomy is a very rare complication.