Objective: To investigate the effects of Lycium barbarum polysaccharide (LBP) on experimental gastric ulcers in rats.Methods: The ulcers were induced by water-immersion restraint stress, acetic acid and pylorus-ligation in rats. In each model, animals were divided randomly into 4 groups and administrated with LBP of 100 mg/kg and 300 mg/kg, ranitidine 100 mg/kg (as a reference standard) and saline respectively. Mucosal lesions were scored as ulcer index. In the pylorus-ligation model, we also compared the gastric juice volume, total acidity, acid output and pepsin activity among groups.Results: Oral administration of LBP inhibited the formation of the acute gastric lesions induced by physical stress such as water-immersion restraint (P<0.05), and accelerated the healing of chronic gastric ulcer model induced by acetic acid (P<0.05 to P<0.01). In the pylorus-ligated rats, significant decrease was also seen in ulcer index (P<0.05 to P<0.01), total acidity (P<0.05), acid output (P<0.05 to P<0.01). LBP 300 mg/kg even showed marked reduction of the volume (P<0.05) and pepsin activity (P<0.05) in the gastric juice. These effects were in a dose-dependent manner. Conclusion: LBP has protective effects on treating gastric ulcer and this action may relate to the reduction of acid output and pepsin activity in the gastric juice.