Protein-losing enteropathy denotes the excessive loss of plasma protein into the gastrointestinal tract, causing edema and hypoproteinemia without albuminuria or evidence of liver disease. In primary protein-losingenteropathy, the protein loss is not attributable to any specific underlying disorder. This condition is associated with unexplained dilatation of the lymphatic channels of the small intestine. A biopsy-proved case of primary protein-losing enteropathy in a 24-year-old man is reported with brief review of literatures. Leakage of chyle into the gut lumen was observed by means of lymphography.