AIM: To investigate the dynamic functional and ultrastructural changes of gastric parietal cells induced by water immersion-restraint stress (WRS) in rats.METHODS: WRS model of Sprague-Dawley (SD) rats was established. Fifty-six male SD rats were randomly divided into control group, stress group and post-stress group. The stress group was divided into 1, 2 and 4 h stress subgroups. The post-stress group was divided into 24, 48 and 72 h subgroups. The pH value of gastric juice, ulcer index (UI) of gastric mucosa and H+, K+- ATPase activity of gastric parietal cells were measured.Ultrastructural change of parietal cells was observed under transmission electron microscope (TEM).RESULTS: The pH value of gastric juice decreased time-dependently in stress group and increased in poststress group. The H+, K+-ATPase activity of gastric parietal cells and the UI of gastric mucosa increased time-dependently in stress group and decreased in poststress group. Compared to control group, the pH value decreased remarkably (P = 0.0001), the UI and H+, K+-ATPase activity increased significantly (P = 0.0001, P =0.0174) in 4 h stress subgroup. UI was positively related with stress time (r = 0.9876, P ＜ 0.01) but negatively with pH value (r = -0.8724, P ＜ 0.05). The parietal cells became active in stress group, especially in 4 h stress subgroup, in which plenty of intracellular canalicular and mitochondria were observed under TEM. In post-stress group, the parietal cells recovered to resting state.CONCOUSION: The acid secretion of parietal cells is consistent with their ultrastructural changes during the development and healing of stress ulcer induced by WRS and the degree of gastric mucosal lesions, suggesting gastric acid play an important role in the development of stress ulcer and is closely related with the recovery of gastric mucosal lesions induced by WRS.