This study was conducted in order to examine the effects of Sapindus mukorossi Leaf Extracts (SME) on lipid synthesis in 3T3-L1 cells. Treatment with SME resulted in inhibition of lipid synthesis in 3T3-L1 cells. In addition, treatment with SME resulted in dose-dependent suppression of adipogenesis/lipogenesis-related protein expression levels of peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT/enhancer-binding protein-α (C/EBP-α), sterol regulatory element-binding protein-1c (SREBP-1c), fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), MAPKs, and NF-κB. Furthermore, treatment with SME resulted in increased phosphorylation of AMP-activated protein kinase (AMPK) involved in lipid metabolism. These findings suggest that inhibition of adipocyte lipid synthesis by SME occurs through suppression of adipogenesis/lipogenesis-related protein expression and activation of the AMPK pathway. Therefore, based on these findings there is potential for use of SME as a natural material for prevention of obesity.