A 62-year-old man was suffering from asymptomatic gross hematuria. Abdominal computed tomography demonstrated a horseshoe kidney and renal pelvic tumor in the left kidney. Open nephrectomy with division of the isthmus was performed. The pathological diagnosis was urothelial carcinoma, grade 2＞ grade 3, pT3. He is free of disease at 13 months after operation. To our knowledge, in Japan, this is the 33th case of renal pelvic tumor in a horseshoe kidney.