A freeze-dried aqueous extract from red mangrove bark was studied in rats for ability to inhibit gastric secretion and to protect gastroduodenal mucus against injury caused by pyloric ligation, hypothermic-restraint stress, indomethacin and cysteamine administration, and chronic ulcers produced by topical application of acetic acid on gastric wall. An oral dose of 500 mg/kg of the lyophilized extract showed antiulcerogenic activity in rats subjected to indomethacin, pyloric ligation, and cysteamine administration. No significant effect was found in hypothermic-restraint stress. The freeze-dried extract from red mangrove not only presented antiulcerogenic properties in acute experimentally induced gastric lesions in rats, but it also showed a significant decrease in lesion index (p < 0.05) in a chronic ulcer model produced by acetic acid in gastric walls, thus demonstrating its healing properties.