Arctium lappa L. is used in folk medicine as a diuretic, depurative and digestive stimulant and in dermatological conditions. The objective of this study was to evaluate the effect and the possible mechanisms involved in the gastroprotective effects of a chloroform extract (CE) of the roots from A. lappa and its fractions. Oral pretreatment with CE (10, 30 and 100 mgkg-1) significantly reduced gastric lesions induced by ethanol by 61%, 70% and 76%, respectively. Oral administration of CE (100 mgkg-1 per day for 7 days) reduced the chronic gastric ulceration induced by acetic acid by 52%. Intraduodenal CE (100, 300 and 600 mgkg-1) reduced the total acidity of gastric secretion by 22%, 22% and 33%, respectively, while i.p. administration (10, 30 and 100 mgkg-1) inhibited total acidity by 50%, 60% and 67%, respectively. In-vitro, CE inhibited H+, K+-ATPase activity with an EC50 of 53 μgmL-1 and fraction A (30 and 100 μgmL-1) reduced this by 48% and 89%, respectively. CE had no effect on gastrointestinal motility. CE (250 μgmL-1) and fraction B (100 and 250 μgmL-1) had free-radical scavenging ability, inhibiting 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical activity by 50%, 20% and 55%, respectively. Collectively, the results show that the CE protects animals from gastric lesions by reducing gastric acid secretion via inhibition of gastric H+, K+-ATPase.