PURPOSE: To provide an antiulcerous agent containing as an active ingredient the organic solvent extract or organic solvent aqueous solution extract of Hypericum erectum thumb used as external agents for hemostasis, swellings, etc., also as decoctions for menoxenia, sedation, etc.

CONSTITUTION: This antiulcerous agent contains as an active ingredient the organic solvent extract or organic solvent aqueous solution extract of Hypericum erectum Thumb, the extract being obtained by grinding the whole grasses of the Hypericum erectum Thumb preferably collected in the seasons ranging from summer to autumn after dried or not dried and subsequently extracting the ground product at the ordinary temperature or at a heated temperature. The extract is extremely low toxic and highly safe. This agent has an activity to prevent especially acute gastritis models, and exhibits remarkable effects on aspirin or ethanol induced tunica mucosa lesions of stomack, especially on the latter lesions. Namely, the agent has a prevention factor-reinforcing action.