The composition of the present invention comprises (1) a biologically effective amount of an extract of a plant of the genus Eucalyptus as an active ingredient, and (2) a biologically acceptable carrier or diluent, and is effective for inhibiting or preventing obesity (increase in weight), lipid storage disease, hyperlipemia, arteriosclerosis, or thrombosis, and is also effective for inhibiting or reducing an amount of triglyceride or an amount of cholesterol in blood. Therefore, the composition of the present invention is used in the form of drugs, food products, food additives, animal feeds, and additives for animal feeds.