Obesity-associated focal segmental glomeruloscleropis(OB-FSGS) has been known to progress into advanced renal insufficiency, and its clinicopathological features Include obesity, FSGS lesions with glornerulomegaly and, nephrotic-range proteinuria without edema. A 14 year old girl with Prader-Willi syndrome showed nephrotic-range proteinuria without hypoalbuminemia or edema. The renal biopsy revealed focal segmental glomerulosclerosis together with glomerular hypertrophy and an increased mesangial matrix. We report here a case of OB-FSGS as one of the renal problems of Pradel-Willi syndrome, and we came to the conclusion that Prader-Willi syndrome is one of the Possible disease entities that can lead to renal insufficiency through obesity.