This experimental study was designed to investigate the effects of Seunggijoui-tang on the weight of obese rats induced by high fat diet. A series of experiments have been conducted in order to measure the effects of above the body weight, serum and fat cell. The measurements have been performed on; (1) the increasing amount of body weight; (2) the quantity of total cholesterol, triglyceride, free fatty acid, total lipid, phospholipid, HDL-cholesterol and LDL-cholesterol in serum; (3) the size of the epididymal fat cell and the fat drops area in hepatic lobule. In the SG I (Group fed high fat diet and administered 42.5mg/100g extract of Seunggijoui-tang during 8 weeks), the weight decreased significantly throughout the whole research period. In the SG I & SG II (Group fed high fat diet and administered 85mg/100g extract of Seunggijoui-tang during 8 weeks), the serum total cholesterol, triglyceride, total lipid, phospholipid, LDL-cholesterol decreased significantly in comparison with control group. In the SG I, the serum free fatty acid decreased significantly in comparison with control group. In the SG I & SG II, the serum HDL-cholesterol decreased in comparison with control group, but this result showed no efficacy. In the SG I, the epididymal fat cell decreased significantly in comparison with control group. In the SG II, the fat drops area in hepatic lobule of rats decreased significantly in comparison with control group. Based on the above result, it is assumed that the clinical application of Seunggijoui-tang can help the treatment of obesity.