Objectives : Although Yeoldahanso-tang (YDHST) has been widely used for treatment of obesity and its related diseases such as hyperinsulinemia and hypertension for Taeeumin, no scientific evidence has reported yet to support its ability to work against these metabolic disorders. Our study was aimed to investigate the anti-obesity effect of YDHST extract on the cellular differentiation of 3T3-L1 preadipocytes into adipocytes. Methods : 3T3-L1 preadipocytes were differentiated into adipocytes by adding insulin, dexamethasone and 3-isobutyl-1-methylxanthine (IBMX) for 8 days in the absence or presence of YDHST extract. Anti-obesity effects of YDHST extract were evaluated by Oil Red O staining, glycerol-3-phosphate dehydrogenase (GPDH) activity, triglyceride contents, and leptin production. Results : YDHST extract remarkably prevented lipid accumulation with no cytotoxicity in the differentiated 3T3-L1 cells. In addition, YDHST extract decreased contents of triglyceride 3T3-L1 adipocytes. Consistently, YDHST extract caused a significant inhibition of GPDH activity and leptin production in a dose-dependent manner. Conclusions : Our findings suggest that Sasang constitutional herbal formula YDHST for Tae-eumin has anti-obesity activity by regulation of the adipogenesis process in vitro. Additional study will be required to further confirm the inhibitory effect on adipocyte differentiation by using in vivo animal model.