Bioactivity-guided fractionation ofF. drupaceaThunb. extract revealed that the water fraction (FDWF) increased pH of the artificial gastric juice from 1.2 to 5.67 ± 0.015. The gastroprotective effect of FDWF against ulcer induced by ethanol was evaluated in rats. In ulcerogenic rats, increase in the gastric juice volume and ulcer lesions, and decrease in the gastric pH were evident. However, pretreatment with FDWF (100 mg/kg b.wt., p.o.) significantly inhibited lesion index, reduced gastric juice volume by 56.09% and increased gastric pH value. When given after ethanol, the same dose of FDWF led to significant healing of the gastric ulcer, with 75.60% reduction of gastric juice volume, and increase in pH value. In both prophylactic and therapeutic-treated groups, the level of superoxide dismutase and reduced glutathione in gastric homogenate were increased, while that of malondialdehyde was decreased. Also, the levels of succinate dehydrogenase and lactate dehydrogenase were increased, while that of acid phosphatase was decreased. In addition, the inflammatory markers; IL-10 and PGE2 were significantly increased. The histopathological results confirmed the above findings and indicated that the antiulcer effect of FDWF is mediated, at least in part, through antioxidant and anti-inflammatory mechanisms. Twenty-three compounds were tentatively identified in FDWF using UPLC−PDA−ESI–MS/MS and most of them were found to be phenolic acid derivatives. FDWF was standardized to contain 23.66 ± 2.62 mg/g and 8.86 ± 0.29 mg/g of quinic acid and chlorogenic acid, respectively. Accordingly, FDWF is a potential natural product that could increase the healing of gastric mucosal injury and prevents the development of ethanol-induced gastric mucosal injury in rats.