Helicobacter pylori-colonized Mongolian gerbils prepared by oral inoculation of a broth culture obtained from a liquid culture of Helicobacter pylori, to the Mongolian gerbils for intragastric colonization of Helicobacter pylori. These Mongolian gerbil models are useful for screening the therapeutic efficacies of drugs against Helicobacter pylori, as well as elucidation of pathology of Helicobacter pylori disease in humans. Moreover, the medium of the present invention for isolating Helicobacter pylori, which is supplemented with vancomycin, trimethoprim, amphotericin B, polymyxin B and 2,3,5-triphenyltetrazolium chloride, enables selective and efficient detection of Helicobacter pylori colonized in their Mongolian gerbils which have microorganisms living in stomach. A combined use of the above-mentioned Mongolian gerbil models and the medium for isolating Helicobacter pylori enables screening of an anti-Helicobacter pylori substance at an animal levels thereby enabling accurate prediction of clinical effects of the anti-Helicobacter pylori substance.