PURPOSE: To obtain the subject agent having anti-Helicobacter pyrori action and useful as an agent for the treatment and the relapse prevention of digestive ulcer, gastritis and hepatitis.

CONSTITUTION: This anti-Helicobacter pyrori agent contains nordamnacanthal of formula I or damnacanthal of formula II. Nordamnacanthal is an orange acicular crystal having a melting point of 215.5-219.0°C (recrystallized from CHCl3-hexane) and damnacanthal is a yellow acicular crystal having a melting point of 215.0-216.9°C (recrystallized from CHCl3-hexane). The compounds of formula I and formula II can be produced by extracting dried roots of Morinda citrifolia with an organic solvent (preferably MeOH or CHCl3) or water at room temperature or under heating preferably after pulverizing the roots, filtering the extract and distilling out the solvent from the filtrate under reduced pressure. The daily administration rate of the agent for adult is generally 0.10-3,000mg, preferably 1-1,000mg divided in 1-4 divided portions.