We report an 18-year-old woman with acute myelomonocytic leukemia, who developed massive lower intestinal bleeding following induction chemotherapy. Colonoscopy revealed multiple circular ulcers but no infectious colitis or infiltration of leukemia. The biopsy specimen showed mild non-specific inflammatory changes and scattered apoptosis bodies. She took nonsteroidal anti-inflammatory drugs (NASIDs) for pyrexia and pharyngalgia for a long time. We concluded these were signs of ulcers induced by NSAIDs. Despite discontinuance of NSAIDs, melena did not improve. Transarterial embolization therapy using microcoils was tried with unsatisfactory results. Finally, colonoscopic clipping therapy and continuous arterial injection of vasopressin were performed. Subsequently, her condition improved markedly. In conclusion, NSAID-induced intestinal bleeding is not limited to the upper GI tract but may occur in the lower GI tract after long-term NSAID use. The possibility of lower GI tract complications from NSAID should be kept in mind.