We report a case of left essential renal hematuria successfully treated with the instillation of hydrogen peroxide into the renal pelvis. A 68-year-old man was referred to our hospital with the chief complaint of gross hematuria. Our diagnosis was left renal essential hematuria. We could not find the bleeding point using a flexible ureteroscope. Due to prolonged gross hematuria, we performed instillation of hydrogen peroxide into the renal pelvis and the gross hematuria completely disappeared. Retrograde hydrogen peroxide instillation therapy is useful and safe for essential renal hematuria.