The aim of this study was to determine the changes in the function and fine structure of the gastric mucosa following exposure to high cadmium (Cd) for 30 d in rats. in the present study, control animals were fed with normal food and tap water and the remaining animals received Cd (15 ppm CdCl2) in drinking water for the same period. Receiving Cd for 30 d increased the mean blood (p < 0.01) and mucosa (p < 0.001) Cd levels, while decreased mucus thickness, mucin content (p < 0.01) significantly. Basal acid output fell significantly (p < 0.01). Light and electron microscopic examination revealed the following: (1) Cd decreases the mean number of surface mucous, isthmic-neck, parietal cells (p < 0.05) and chief cells (p < 0.001) per unit from the control value and (2) in some cells of zymogenic unit, the Cd-induced alterations were characterized with dilated Golgi cisternae, focal enlarged endoplsmic reticulum, broken tubulovesicles, degenerated mitochondria, dense nuclei, as well as lysosomal structures. We concluded that Cd augments the elimination rate of zymogenic unit's cells by increasing the alteration rate, and the reduced basal acid output, mucin content, and mucus thickness can be explained easily with the loss of zymogenic unit's cell population.