Hemorrhagic cystitis is a complication of systemic lupus erythematosus and is also a common side effect after cyclophosphamide therapy. Intractable hemorrhagic cystitis is not unusual and may be a life-threatening condition; it has no effective noninvasive treatment at present. We report a case of hemorrhagic cystitis with intractable refractory bleeding that occurred in a 40-year-old woman after cyclophosphamide treatment for systemic lupus erythematosus. The hemorrhage was resistant to various therapies but resolved after hyperbaric oxygen therapy. There was no recurrent hematuria after hyperbaric oxygen therapy during 6 months of follow-up.