Background : Obesity, the syndrome caused by a high fat diet, is a disease. At the same time, obesity causes diabetes mellitus, hyperlipidemia, and cardiovascular disease. Recently, its prevalence rate is increasing. Yagwan-cheunghyeoltang (YCT) used in this experiment is the prescription of Yagwanmoon added to Cheunghyeol-tang which is reported to be very effective in weight loss controlling and serum cholesterol. It is also reported that Yagwanmoon has significant antioxidant effects and YCT has a significant effect on blood glucose control. Objectives : This study was conducted to experimentally evaluate the effects of YCT on obesity in rats induced by high fat diet. Methods : The experiment was conducted with 4-week-old male rat s divided into 5 groups. They were a normal diet group, a high fat diet group, a positive drug control group, a 1% YCT group, and a YCT 3% group, and were tested for eight weeks. After four weeks of inducing obesity by a high fat diet, rats were allowed to lose weight by following the normal diet group, approximately 30% compared with 10 rats in each group were determined as still obese. Changes in body weight and organ weight and serum cholesterol, triglyceride, glucose-density, low density lipoprotein cholesterol, antioxidant activity were checked. Results : In the experimental groups, we observed weight loss and visceral fat reduction, improvement of liver function, reduction of serum glucose, activation of HMG-CoA reductase inhibitor, reduction of concentrations of leptin and it showed a significant effect on antioxidants and lipid peroxidation. Conclusions : YCT has significant effects on the regulation of hyperlipidemia and lipid peroxidation associated with obesity and has significant effects on, antioxidants and lipid peroxidation, too. Additional clinical studies are needed.