Radiation-induced hemorrhagic cystitis is a refractory disease that can cause severe hematuria and bladder tamponade. Bladder tamponade due to radiation-induced hemorrhagic cystitis can often recur repeatedly and markedly reduce the quality of life. However, no blood test parameter has been studied yet regarding the prevention of bladder tamponade recurrence. An 84-year-old patient with a history of radiation therapy for cervical cancer was repeatedly hospitalized for bladder tamponade due to radiation-induced hemorrhagic cystitis. At each hospitalization, blood transfusions were performed to treat severe anemia as the first treatment, resulting in hematuria improvement, and the patient was discharged without invasive treatments such as transurethral coagulation. However, anemia developed gradually after each discharge. The anemia progression was obviously unrelated to macrohematuria because macrohematuria did not appear during that period. When the serum hemoglobin level decreased below the physiological range, bladder tamponade recurred. Based on these findings, we posited that the monitoring of the serum hemoglobin level could be useful to predict the occurrence of bladder tamponade. We hypothesized that if the serum hemoglobin level did not fall below the physiological range, bladder tamponade would not occur. We treated chronic anemia after determining its cause and kept serum hemoglobin levels within the physiological range. Since the treatment was initiated, bladder tamponade has not recurred in over 27 months. In this case, the monitoring of the serum hemoglobin level was useful to predict the occurrence of bladder tamponade due to radiation-induced hemorrhagic cystitis. By maintaining serum hemoglobin levels within the physiological range, we successfully prevented the recurrence of bladder tamponade due to radiation-induced hemorrhagic cystitis.