Lymphangiectasia of the large intestine associated with protein-losing enteropathy is reported. A 33-yr-old man suffered from diarrhea, sometimes mixed with blood. Colonoscopic study revealed reddish and edematous mucosa with multiple flat elevated lesions and giant folds in the localized segment of the rectosigmoid. An intestinal clearance test of alpha 1-antitrypsin revealed the association of protein-losing enteropathy. Operation was performed successfully, resulting in a marked improvement of symptoms and laboratory data, especially serum total protein, albumin, IgG, and Leu-2a-positive cells (suppressor/cytotoxic T cells). Giant folds consisted of the submucosal edema and hyperplasia of the epithelial glands with cystic dilatation of glands, and flat elevated lesions consisted of mucosal and submucosal edema associated with intestinal lymphangiectasia, adipose tissue, and blood capillaries. The population of the Leu-2a-positive cells in the lamina propria and intraepithelial layer was decreased and that of the Leu-3a-positive cells (helper/inducer T cells) in the lamina propria was increased.