This study examined the inhibitory effects of 4-guanidinobutyric acid (4GBA), an alkaloid, against gastric lesions by assessing the inhibition of Helicobacter pylori (H. pylori) and gastric cancer cells. Acute and chronic gastritis were also observed using HCl/ethanol (EtOH) and indomethacin-induced gastric lesion models, respectively. 4GBA inhibited the growth of H. pylori in a dose dependent manner, and showed acid-neutralizing capacity. In the pylorus ligated rats, 4GBA decreased the volume of gastric secretion and gastric acid output slightly, and increased the pH. 4GBA at a dose of 100 mg/kg reduced the size of HCl/EtOH-induced gastric lesions (70.8%) and indomethacin-induced gastric lesions (38.8%). The antigastritic action of 4GBA might be associated with the acid-neutralizing capacity, anti-H. pylori action, and decreased volume of gastric secretion. These results suggest that 4GBA might be useful in the treatment and/or protection of gastritis.