AIM: To investigate the bactericidal effects of Chenopodium ambrosioides L.(CAL) against Helicobacter pylori(H.pylori) both in vitro and in vivo.METHODS: For in vitro experiments, the inhibitory activity of CAL was tested using an agar dilution method; H.pylori strain NCTC11637 was incubated on Columbia blood agar plates containing serial concentrations of CAL.The minimal inhibitory concentration(MIC) was determined by the absence of H.pylori colonies on the agar plate.Time-kill curves were used to evaluate bactericidal activity; the average number of colonies was calculated at 0, 2, 8 and 24 h after liquid incubation with concentrations of CAL at 0.5, 1, and 2 × MIC.For in vivo experiments, H.pylori-infected mice were randomly divided into CAL, triple therapy(lansoprazole, metronidazole, and clarithromycin), blank control, or H.pylori control groups.The eradication ratios were determined by positive findings from rapid urease tests(RUTs) and by histopathology.RESULTS: In vitro, the MIC of CAL against H.pylori was 16 mg/L.The time-kill curves showed a stable and persistent decreasing tendency with increasing CAL concentration, and the intensity of the bactericidal effect was proportional to dose; the 1 and 2 × MIC completely inhibited the growth of H.pylori at 24 h.In vivo, the eradication ratios in the CAL group were60%(6/10) by RUT and 50%(5/10) by histopathology.Ratios in the triple therapy group were both 70%(7/10), and there was no difference between the CAL and triple therapy groups.Histopathologic evaluation revealed massive bacterial colonization on the surface of gastric mucosa and slight infiltration of mononuclear cells after inoculation with H.pylori, but no obvious inflammation or other pathologic changes in gastric mucosa of mice from CAL and triple therapy groups.CONCLUSION: CAL demonstrates effective bactericidal activity against H.pylori both in vitro and in vivo. To investigate the bactericidal effects of Chenopodium ambrosioides L. (CAL) against Helicobacter pylori (H. pylori) both in vitro and in vivo. METHODS: For in vitro experiments, the inhibitory activity of CAL was tested using an agar dilution method; H. pylori strain NCTC11637 was incubated on Columbia blood agar plates containing serial concentrations of CAL. The minimal inhibitory concentration (MIC) was determined by the absence of H. pylori colonies on the agar plate. Time-kill curves were used to evaluate bactericidal activity ; the average number of colonies was calculated at 0, 2, 8 and 24 h after liquid incubation with concentrations of CAL at 0.5, 1, and 2 × MIC. For in vivo experiments, H. pylori-infected mice were divided divided into CALs , triple therapy (lansoprazole, metronidazole, and clarithromycin), blank control, or H. pylori control groups. The eradication ratios were determined by positive findings from rapid urease tests (RUTs) and by histopathology .RESULTS: In vitro, the M IC of CAL against H. pylori was 16 mg / L. The time-kill curves showed a stable and persistent decreasing tendency with increasing CAL concentration, and the intensity of the bactericidal effect was proportional to dose; the 1 and 2 × the growth of H. pylori at 24 h. vivo, the eradication ratios in the CAL group were 60% (6/10) by RUT and 50% (5/10) by histopathology. Ratios in the triple therapy group were both 70% (7/10), and there was no difference between the CAL and triple therapy groups. Histopathologic evaluation of massive bacterial colonization on the surface of gastric mucosa and slight infiltration of mononuclear cells after inoculation with H. pylori, but no obvious inflammation or other pathologic changes in gastric mucosa of mice from CAL and triple therapy groups. CONCLUSION: CALACTIVE effective bactericidal activity against H. pylori both in vitro and in vivo.