Objectives To investigate anti-obesity effects of Galgeun-tang, an herbal formula, in high fat diet induced obese mice model. Methods 24 Male C57Bl/6J mice were randomly assigned to normal group fed with normal research diet (NOR, n=6), high fat diet control group treated with water (HFD, n=6), high fat diet group treated with Orlistat (ORL, n=6, Orlistat 10 mg/kg), and high fat diet group treated with Galgeun-tang (GGT, n=6, Galgeun-tang 700 mg/kg). 12 weeks later, body weight, fat weight, liver weight, blood glucose, total cholesterol, triglyceride, HDL, ALT, AST, obesity related neuropeptides and adipokines, ratio of gut microbiota, and histopathology of liver were evaluated. Results In the GGT group, 1. body weight gain, liver weight gain, and total fat weight gain were significantly less than those in the HFD group. 2. blood glucose level was significantly lower and insulin level was significantly higher than in the HFD group. 3. total cholesterol level and triglyceride (TG) level were significantly lower and high density lipoprotein (HDL) level was significantly higher than in the HFD group. 4. appetite-promoting ARC neuropeptides such as Agrp and Npy were significantly less and appetite-inhibiting ARC neuropeptide, Cart was significantly more than in the HFD group in qRT-PCR analysis. 5. adiponectin level and visfatin level were significantly higher, and resistin level and leptin level was significantly lower than in the HFD group. 6. the relative level of Bacteroidetes was significantly higher, and the relative level of Firmicutes was significantly lower than in the HFD group. 7. the increase of adipose tissue was significantly more inhibited than in the HFD group. Conclusions The present study showed that Glageun-tang exerts anti-obesity effects in that it. 1. inhibited the increase in body weight, liver weight, and total fat weight. 2. decreased the level of TG, and increased the level of HDL. 3. influenced neuropeptides and adipokines that are important in regulating food intake and changes of body weight. 4. modified the beneficial quantitative changes in gut microbiota suppressing the tendency toward obesity.