Focal segmental glomerulosclerosis (FSGS) is extremely rare among paraneoplastic nephrotic syndromes. We herein report a case of lung adenocarcinoma with nephrotic syndrome caused by paraneoplastic FSGS. A 68-year-old man visited our hospital for an evaluation of a right hilar mass on chest radiography and supraclavicular lymphadenopathy. Because an aspiration biopsy of the supraclavicular lymph node revealed adenocarcinoma, the patient was diagnosed with lung adenocarcinoma. He also had nephrotic syndrome, and the pathological findings of the renal biopsy demonstrated FSGS. Standard-dose carboplatin-containing chemotherapy led to a partial response for lung cancer and improved the patient's nephrotic syndrome without causing any adverse renal effects.