Obesity is associated with numerous diseases such as type 2 diabetes, hypertension and cancer. Inhibition of adipogenesis is a effectite strategy to anti-obesity. In this study, Galla Chinenisis extract (GCE) inhibited adipocyte differentiation in OP9 cells. There was no cytotoxicity when cells were treated with GCE in designated time intervals, unaffected by concentration. In this cell model, increases in fat storage were inhibited by 2 days treatment with various concentration of GCE, visualized by Oil red-O, BODIPY and DAPI staining. To understand the underlying mechanism at the molecular level, the effects of GCE were examined on the expression of the genes involved in adipogenesis by real-time PCR. In the progress of adipocyte differentiation with GCE-treated, the mRNA level of adipogenic genes such as peroxisome-proliferator-activated receptors gamma ($PPAR{gamma}$), computer-assisted axial tomography/enhancer binding protein-alpha ($C/EBP{alpha}$) were decreased. Also, GCE treatment inhibited increase of mRNA expression, which is adipogenic factor such as fatty acid synthase (FAS), hormone-sensitve lipase (HSL), lipoprotein lipase (LPL), and adipocyte-specific lipid binding protein (aP2). Therefore, the result of this study suggest that Galla Chinenisis extract can prevent adipocyte differentiation and GCE may have a great potential as a novel anti-adipogenic agent.