BACKGROUND Chylothorax is a state in which pleurisy is induced by chylomicron leakage due to lymphatic injury. Membranous nephropathy (MN) is one of the relatively common glomerular diseases that cause nephrotic syndrome in adults. Chylothorax at the onset of nephrotic syndrome is very rare in adult patients. METHODS We report a case of chylothorax associated with primary MN. A 64-year-old man visited the hospital complaining of lower extremity edema and dyspnea for 4 weeks. Laboratory findings showed no azotemia but hypercholesterolemia, hypoalbuminemia, nephrotic-range proteinuria, and microscopic hematuria. Chest and abdominal computed tomography (CT) revealed no ascites, venous thrombosis, or malignancy with the presence of right-side pleurisy. Biochemical analysis of the pleural fluid was consistent with chylothorax. The patient was confirmed to have MN by percutaneous kidney biopsy. An angiotensin receptor blocker, diuretics, and a hypolipidemic agent were prescribed; non-per os, total parenteral nutrition (TPN), and subcutaneous injection of octreotide were added for management of chylothorax. As serum anti-phospholipase receptor 2 antibody (Ab) concentration increased again, immunosuppressive therapy (IST) consisting of alternating monthly cycles of glucocorticoids and oral cyclophosphamide was instituted. With no improvement in chylothorax and deteriorating nutritional status despite 3 weeks of medical therapy, lymphangiography was performed, followed by thoracic duct embolization (TDE). The patient was discharged from the hospital on day 53 with clinical improvement. At 9 months after discharge, clinical remission of primary MN was achieved without recurrence of chylothorax. CONCLUSIONS Patients with nephrotic syndrome may rarely exhibit refractory chylothorax without chylous ascites, increasing the risk of serious metabolic complications such as severe malnutrition. Therefore, upon confirming chylothorax associated with primary nephrotic syndrome, prompt radiologic intervention for lymphatic leakage must be considered in addition to specific IST.