Objectives This study was designed to evaluate the efficacy of Seungyangjeseup-tang on obesity by using 3T3-L1 cells and high fat diet mice. Methods In vitro, Seungyangjeseup-tang extract (SYJST) (10, 50, 100, 200, 400, 800μg/mL) ware added in 3T3-L1 cells. SYJST cytotoxicity was measured by 3-(4,5 -dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assasy. Adipocyte differentiation was measured by Oil Red-O staining. In vivo, the experimental animals were divided into five groups: normal diet-fed normal group (N), high-fat diet (HFD)-fed control group (Con), HFD+SYJST 100 mg/kg group (SY100), HFD+SYJST 200 mg/kg group (SY200), and HFD+olistat 60 mg/kg as a positive drug control group (Orli). Markers of obesity, such as body weight, liver weight, food intake, serum total cholesterol (TC), triglycerides (TG), high density lipoprotein cholesterol (HDL-C), liver tissue TC, TG and fecal TC, TG were measured. Results In vitro, cytotoxicity was not significant compared with the control group. 3T3-L1 cell's differentiation was significantly decreased in Oil Red-O staining. In vivo, compared with controls, mice treated with SYJST demonstrate lower body and liver weight, and reduced food intake. In addition, SYJST increased TC, TG in the serum but not significance. And SYJST showed decreasing tendency TC, TG in the liver tissue. Furthermore, SYJST increased TC, TG in the facal but not significance. Conclusions Based on the results above, Seungyangjeseup-tang may reduce adipocyte differentiation, body fat, food intake, liver weight in obesity. This suggests that Seungyangjeseup-tang may be clinically useful in obesity treatment. (J Korean Med Rehabil 2018;28(3):1-11)