Yellow nail syndrome is a rare disease with unknown etiology, Attributed to functional anomalies or disturbance in lymphatic drainage. This condition is characterized by triad of nail discoloration, respiratory or intrathoracic manifestations and lymphedema.Twenty days after mitral valve replacement for severe rheumatic mitral valve stenosis, 39 years old woman presented with face tenderness and hearing problems besides stuffy and clogged nose and underwent routin rhinosinusitis therapy. She came back to ears, nose and throat service with persistent rhinosinusitis as well as relapsing preoperative couphs and dyspnea besides lower extremities edema and toenails discoloration. After some modulations of treatment, she was introduced to pulmonary clinic on post -operative day = 30. Chest x ray showed a lot of left pleural effusion then she was returned to our service (cardiac surgery) on post- operative day = 33. The pigtail catheter was secured and we attained a significant amount of milky fluid which conformed with chylothorax. Finally Yellow nail syndrome was diagnosed with her on post-operative day = 35. Early conservative therapy such as bed rest, legs massage, low fat diet with medium chain triglycerides, diuretics, bronchodilator inhaler was not be able to satisfy us (chylous out put > 330 cc/d). Therefore the catheter replacement with chest tube was carried out followed by pleurodesis using Talc and doxycycline besides transition of oral intake to total parentral nutrition and vitamine E supplement, on post - operative day = 41. After that chylous leakage gradually subsided and patient was discharged to home on post- operative day = 47. At 4 weeks follow ups, chest x ray was clear without effusion and nails discoloration and legs lymphedema resolved.We reported the third post cardiac surgery Yellow nail syndrome which is an unclear entity with a set of associated signs and symptoms. Two prior reports involved with coronary artery bypass graft whereas we performed mitral valve replacement. In angiogram thoracic duct was not identified so that it seems post cardiac surgery Yellow nail the syndrome has iatrogenic origin due to the thoracic duct or its tributaries injury and requires meticulous assessment and management.