Internal hernia is defined as the herniation of viscera through an anatomic or pathologic opening within the boundaries of peritoneal cavity. Transmesocolic hernia, a subtype of internal hernia, has a herniated sac through the transverse mesocolon. Transmesocolic hernia has been rarely described in the literature, and most of reported cases were associated with a history of operation or congenital anormaly. A 72-year-old female with chronic intermittent abdominal pain and bloating was admitted. Small bowel series showed multiple jejunal loops confined to the left upper quadrant of abdomen. Abdomen spiral computed tomography (CT) showed a cluster of mildly dilated small bowel loops with mesenteries on the same area. On the three-dimensional reconstruction CT scan, a herniated sac through the transverse mesocolon was identified. She was diagnosed as transmesocolic hernia by using the three-dimensional reconstruction CT and small bowel series, without surgical exploration. The symptoms were managed with conservative measures.