The anti-Helicobacter pylori (H. pylon) activity of a water extract of Chinese chive (Allium tuberosum) (WCC) was investigated. On disk diffusion assay, WCC effectively inhibited the growth of all 21 strains tested, including isogenic mutants, showing inhibition diameters of 12 to 29 mm, irrespective of drug susceptibility and clinical manifestation. The minimum inhibitory concentration (MIC) of WCC was 2.45 mg dry weight/mL. Killing assay with multiples of MIC confirmed that WCC had bactericidal activity and that the inhibitory effects were dose dependent. In addition, to determine whether the inhibitory activity of WCC under severe stress conditions, such as heat and acidity, is altered, the stability of WCC was evaluated. The inhibitory activity of WCC exposed to acidic conditions (pH 1.0 to 6.4) was stable, while heat-treated WCC (100 degrees C, 10 min) showed slightly decreased inhibition activity. On combination assay with antibiotics frequently used in clinical practice, WCC was found to be an innocuous agent for antibiotic activity. These results suggest that daily intake of WCC is able to prevent H. pylori colonization in the stomach, and that it could be applied as adjuvant therapy in H. pylori eradication.