Two rare cases of heavy infection with Anisakis larvae are reported. The patients, a 41-year-old and a 65-year-old man, complained of acute abdominalpain after consumption of raw mackerel. Six whitish and thin thread-like worms were found in the stomack of each patient by gastro-endoscopy. The worms isolated from the stomack wall were identified as Anisakis Tyep-I larvae. The detailed morpholgical characteristics of the larvae were obseved by scanning electron microscopy.