Poncirin was isolated from water extract of the fruits of Poncirus trifoliata and metabolized by human intestinal bacteria. The inhibitory effect of poncirin and its metabolites by these bacteria on the growth of Helicobacter pylori (HP) was investigated. Among them, ponciretin (5, 7-dihydroxy-4'-methoxyflavanone), the main metabolite most potently inhibited the growth of HP, with a minimum inhibitory concentration (MIC) of 10-20 μg/ml. However, poncirin and its metabolites except ponciretin did not inhibit the growth of HP, nor did they inhibit HP urease.