Acute invasive small bowel anisakiasis is an extremely rare cause of small bowel obstruction. The authors report a case of surgically verified small bowel anisakiasis resulting in small bowel obstruction. A 54-year-old man presented with suddenly developed diffuse abdominal pain after ingestion of raw fish. The peripheral blood examination showed leukocytosis without eosinophilia. CT showed a long segment of thickened small bowel accompanied by a focal narrowed portion and combined with ascites. When these findings are noted in patients with a history of recent ingestion of raw or undercooked fish, the diagnosis of small bowel anisakiasis should be considered in order to avoid application of unnecessary surgical treatment, in spite of the severity of the abdominal pain and bowel obstruction.