Smilax sieboldii is one of the Smilax species. A number of Smilax plants have multiple physiologically-active components and anti-inflammatory/anti-oxidant effects. Antiobesity effects induced by Smilax sieboldii have not been reported. In this study, we investigated the effects and molecular mechanisms of anti-obesity activity of 70% ethanol Smilax sieboldii extract (SSE). The anti-obesity effect of SSE was determined using 3T3-L1 adipocytes. We confirmed that SSE was not cytotoxic to murine 3T3-L1 preadipocytes, we evaluated SSE dosedependently decreased the accumulation of lipids via an Oil Red O assay and triglyceride assay. These anti-obesity activities of SSE were mediated by the inhibition of adipogenesis-related marker genes (peroxisome proliferator activated receptor-γ, CCAATenhancer-binding protein α, and SREBP1c) and lipogenesisrelated marker genes (fatty acid synthase and aP2). These results suggest that SSE has the potential to exert anti-obesity and antihyperlipidemia effects by regulating adipogenic transcription factors and inhibiting the expression of adipogenic markers.