The aim of the study was to demonstrate the influence of immersion and restraint stress on the ultrastructural changes in gastric acid barrier and parietal cells in rats. Twenty rats were randomly divided into control and stress groups. The gastric mucosal ulcer index was measured. The ultrastructural changes in parietal cells, epithelial cells, epithelial cell junctions, and basal lamina were observed by transmission electronic microscopy. Stress could induce gastric mucosal damage obviously. Parietal cells in a resting state in control group but became active in stress groups with plenty of mitochromosomes and secreting cysts. The cell membrane of epithelium on the luminal surface were were injured with the preservation of tight junction and basal lamina. The results indicated that the stress induced acid secretion of parietal cells, which destroys the luminal surface of the epithelium. It thus suggests the significance of epithelial cell membrane damage in the development of stress ulcer.