A 51-year-old man admitted with abdominal pain was diagnosed with paralytic ileus and treated conservatively. When symptoms persisted, we conducted a laparotomy and found 40 cm of the anal side from Treitz's ligament of the jejunum irregularly mottled by necrosis and conducted partial jejunectomy. Postoperative angiography showed multiple aneurysms in superior and inferior mesenteric arteries. Screening for collagen disease was negative. Blood circulation was reconstructed 43 days after the first operation. Histological evaluation showed the media of resected aneurysmal wall to be segmentally absent, leading to a diagnosis of segmental arterial mediolysis. In aneurysms of abdominal splanchnic arteries, it is important to consider screening these arteries as broadly as possible due to possible segmental arterial mediolysis and the necessity of blood circulation reconstruction.