We investigated the anti-obesity effect of berberine in mice fed a high fat diet and focused on the analysis of adipogenesis in epdidymal adipose tissue. Male C57BL/6J mice were divided into three groups, which were fed either a normal diet (Nor), a high fat diet (HFD), or a high fat diet plus orally administered berberine (0.2 g /kg body weight) (HFD+B) for 8 weeks. Relative to mice in the HFD group, mice in the HFD+B group showed significant reductions in weight gain and adipose tissue weight. Serum triglyceride levels in mice from the HFD+B group were significantly lower than those of the HFD mice, as were the levels of serum insulin and leptin. An effect of berberine to reduce epididymal adipose mass was revealed by H&E staining. Berberine inhibited the high fat diet-induced increase in levels of the proteins CD36 and CCAAT/enhancer-binding protein $alpha$ ($C/EBP{alpha}$) observed in epididymal adipose tissues of mice from the HFD group. These results suggest that berberine has an anti-obesity effect in mice and that the effect is mediated by inhibition of adipogenesis.