Abstract: Objective:To investigate the changes of cell ultrastructure in colic mucosa in post infectious irritable bowel syndrome(IBS) through light microscopy and electron microscopy,and to elucidate their possible roles and clinical significance in intestinal mucosal barrier dysfunction. Methods:In 10 normal controls and 30 patients with post-infective IBS,biopsies were taken from the sigmoid colon.The ultrastructure of cells in colic mucosa and the changes of the mast cells in the paraffin-embedded sections were studied through transmission electron microscopy and analyzed by pathological image software. Results:The colic mucosa showed the integrity of epithelial cell membrane,normal cell shape,the regular distribution of microvilli of different length,developed rough endoplasmic reticulum.Many pieces of microvilli had broken.The aperture between cells were remarkably spacious.A large number of secretory granules,vacuoles were seen in the cytoplasm of goblet cells,mast cells and neuroendocrine cells. Conclusions:There were obvious changes on ultrastructure of cells in colic mucosa,which means IBS may be a gastrointestinal organic disease with ultrastrure alterations in colonic mucosa.The changes play a very important role in intestinal mucosal barrier dysfunction.