The present study investigated the antiobesity and lipid lowering effects of an ethanolic extract of leaves obtained from (200 and 400 mg/kg) and its major compound (rosmarinic acid, 10 mg/kg) in obese mice (C57BL/6) induced by a high-fat diet. Continuous supplementation with extract (200 and 400 mg/kg) for 8 weeks significantly decreased body weight gain (p < 0.05). However, supplementation with rosmarinic acid, a constituent in the extract, produced only a slight reduction in body weight gain compared to the high-fat diet control group. Food intake between the treatment and the high-fat diet groups was similar, which suggested that the plant extract did not suppress food intake. Further, body weight reduction of the treatment groups was not due to a decreased reduction in energy intake. Compared to the high-fat diet-fed group, serum triglycerides, total cholesterol, and low-density lipoprotein cholesterol levels were significantly reduced in the treated groups, while high-density lipoprotein cholesterol levels were not significantly altered. Accumulation of hepatic lipid droplets induced by a high-fat diet was markedly inhibited by extract. In addition, significantly diminished liver malondialdehyde production, and significantly elevated the activities of hepatic superoxidase dismutase. The present study showed that an ethanolic extract prepared from the leaves of can significantly reduce a gain in body weight, enhance antioxidant activity, and possess hypolipidemic and antiobesity effects, thereby protecting against the adverse effects of high-fat diet-induced obesity.