Although renal hypouricemia is mostly asymptomatic, it is known to present a high risk of exercise-induced acute renal failure, especially in young males. However, there is little information regarding the clinical features of urolithiasis as a complication in childhood renal hypouricemia. Here we report a 4-year old female with idiopathic renal hypouricemia who presented with macroscopic hematuria due to obstructive calcium oxalate urolithiasis. She was treated successfully with percutaneous nephrolithotripsy and thereafter hematuria disappeared. Sequence analysis of the patient and her family's URAT1 gene confirmed a nonsense mutation in exon 4 (W258X). To the best of our knowledge, this is the youngest case of hereditary renal hypouricemia caused by URAT1 gene mutation, which was found by hematuria due to calcium oxalate urolithiasis.