Achillea millefolium L. (Compositeae) is used in folk medicine to treat gastric disturbances. Doses of 125, 1500 and 2000 mg/kg protected rats against ulcers induced by ethanol and restraint-in-cold-stress, but not against indomethacininduced ulcers. Injected into the duodenal lumen the extract inhibited the basal acid secretion. Data from studies indicate that the antiulcer activity of A. millefolium must been related to a inhibition of gastric secretion or to a increase of protective factors in gastric mucosa as mucus, bicarbonate and blood flow. In conclusion, this extract effectively protected the gastric mucosa and inhibited gastric acid secretion. Further studies should also be provided for the stimulation of receptors in the parietal cell to elucidate the route whereby the extract produce this action.