To obtain an antioxidant for an organism useful as a medicine manifesting an effect on a disease caused by the in vivo oxidation, e.g. arterio sclerosis, myocardial infarction by formulating Muirapuama as an active ingredi ent.

This antioxidant for an organism is obtained by formulating Muirapuama (a root of shrub belonging to olacaceae family, the original plant of which is exemplified by Liriosma ovata sp.) as an active ingredient. For example, an extract obtained by dipping the thinly cut root of the original plant in 50-99% ethanol, further dipping the residue of the before dipped root in the 50-99 ethanol, and condensing the both extracting liquids to form the extract, is used as the antioxidant. for the organism. The daily dose of the extract is 0.2-3.0g/50kg expressed in terms of the amount of the original crude medicine for a general adult and is administered by dividing into one or several portions.