Background. Oyaksungi-san (OYSGS) is a herbal formula that has been used for treating cardiovascular diseases in traditional Asian medicine. Here, we investigated the antiadipogenic effect of OYSGS extract in 3T3-L1 adipose cells. Methods. 3T3-L1 preadipocytes were differentiated into adipocytes with or without OYSGS. After differentiation, we measured Oil Red O staining, glycerol-3-phosphate dehydrogenase (GPDH) activity, leptin production, mRNA, and protein levels of adipogenesis-related factors. Results. OYSGS extract dramatically inhibited intracellular lipid accumulation in the differentiated adipocytes. It also significantly suppressed the (GPDH) activity, triglyceride (TG) content, and leptin production by reducing the expression of adipogenesisrelated genes including lipoprotein lipase, fatty acid binding protein 4, CCAAT/enhancer-binding protein-alpha (C/EBP-[alpha]), and peroxisome proliferator-activated receptor gamma (PPAR-[gamma]). Furthermore, OYSGS clearly enhanced phosphorylation of AMP-activated protein kinase (AMPK) as well as its substrate acetyl CoA (ACC) carboxylase. Conclusions. Our results demonstrate that OYSGS negatively controls TG accumulation in 3T3-L1 adipocytes. We suggest antiadipogenic activity of OYSGS and its potential benefit in preventing obesity.