In this study, we evaluated 3 extracts ( n-hexane, acetone, and methanol) of Usnea undulata Stirton (Usneaaceae) and 5 isolated compounds [methyl orsellinate (1), methyl β-orsellinate (2), 7-hydroxyl-5-methoxy-6-methylphtalide (3), usnic acid (UA) (4), and salazinic acid (5)] for their inhibitory activity against Helicobacter pylori. The results showed that the n-hexane extract exhibited the strongest activity with the largest inhibition zone ( d = 14 mm). For the isolated metabolites, besides UA that has been reported as a potent anti- H. pylori agent, compounds 1 and 2 showed higher inhibition compared to the reference drugs. Our results demonstrated that U. undulata could be a promising source of potential anti- H. pylori metabolites.