Objectives: Samjunghwan has been known to be effective for the treatment of obesity. To show the effectiveness of Samjunghwan in a more scientific way, Samjunghwan extract was prepared and evaluated in high-fat diet rats by measuring the changes of body weight and lipid metabolism as described below. Methods: 245 g of crushed Samjunghwan was extracted with methyl alcohol. The extract was evaporated under reduced pressure to give 21.8 g. For 30 days, the control group rats were given a high fat diet, while the test group rats were given a high fat diet plus Samjunghwan extract. The normal group rats were given a normal diet. 50 mg of Samjunghwan extract per 1 kg of body weight was added to the diet for the test group rats. Results: The control group rats on a high fat diet gained weight by about 27-28% as compared to the normal group, whereas the test group rats on a high fat diet plus Samjunghwan extract lost weight about 6-8% as compared to the control group. A significant increase of liver weight caused by a high fat diet was also inhibited by the same Samjunghwan extract administration. Similar inhibitory effects on the food intake and on the epididymal adipose tissue weight were observed in the high fat diet rats by the administration of Samjunghwan extract. Serum and liver total lipid levels in the control group on a high fat diet increased significantly as compared to the normal group, whereas their serum and liver levels increased less on a high fat diet plus Samjunghwan extract administered test group than the control group. Impressively, serum leptin levels in the test group decreased almost to the level of the normal group, which was well in accordance with the decreased fat contents in the test group rats. Furthermore, the activities of hepatic acetyl-CoA carboxylase and fatty acid synthetase were increased in the control group, while their activities in the test group on a high fat diet plus Samjunghwan extract decreased nearly to the levels of normal group rats on a normal diet. Conclusions: These results showed that the obesity caused by a high fat diet was effectively inhibited the administration of Samjunghwan extract. Our results also showed that the abnormal lipid metabolism caused by a high fat diet was effectively cured by the administration of Samjunghwan extract.