Duplication of alimentary tract can occur rather uncommon cause of abdominal mass and develop several kinds of acute abdominal complication. Its origin is variously at any level of the alimentary tract from the base of the tongue to the anus, but are most common in the small intestine, especially in the ileocecal region. Their developing mechanism is embryologically defined as vacuole theory by Bremer, 1944. Pathologic characteristics are location of mesenteric border, lining mucosa similar to some portion of alimentary tract with all layers of bowel wall, and muscle layer connecting with contiguous intimating intestinal tract. The author presents a case of giant ileocecal duplication developed in 24 years old male under weight of 3.03 kg without any symptoms until it was found incidentally.