Renal involvement in Churg-Strauss syndrome (CSS) is not uncommon, but nephrotic syndrome is rarely reported in patients with CSS. A 25-year-old woman with a long history of bronchial asthma presented to our hospital with a chief complaint of generalized edema. Laboratory studies revealed normocytic normochromic anemia, marked eosinophilia, positive anti-neutrophil cytoplasmic antibody, hypoalbuminemia, and hypercholesterolemia. Urinalysis showed heavy proteinuria (4+) without significant casts. The 24-hour urinary protein excretion was 6.5 g with a selective index of 0.35. Echocardiography and X-ray of the paranasal sinuses suggested restrictive cardiomyopathy and maxillary sinusitis, respectively. Diagnoses of CSS and nephrotic syndrome were made on the basis of clinical and laboratory findings. Renal biopsy was performed, and pathologic findings revealed focal segmental glomerulosclerosis with mesangiolysis. The patient's clinical symptoms and proteinuria improved markedly after combined treatment with corticosteroids and cyclophosphamide. Herein, we report a case of nephrotic syndrome in a patient with CSS.