Abdominal cocoon syndrome (ACS), also known as idiopathic sclerosing peritonitis and primary sclerosing peritonitis, is a rare condition, causing small bowel obstruction. It was named by Foo in 1978 as ACS. It is characterized by partial or total encasement of the small intestine in a fibro collagenous cocoon-like sac. Neither the cause nor the pathogenesis has been elucidated fully. Thus, the diagnosis of the disease is difficult since clinicians often lack sufficient understanding of the disease. A patient was received with described symptoms of intestinal obstruction. Surgery shows that the entire small intestine and intestinal mesentery were enveloped in a fibro collagenous sac. The surgically released small intestine was only 1 meter long. Thus it was diagnosed as congenital small intestinal dysplasia, a rare case.