We investigated the anti-obesity effect of abietic acid in mice fed a high-fat diet with emphasis on changes in adipogenesis in epididymal adipose tissues. Male C57BL/6J mice were divided into four groups and fed a normal diet, a high-fat diet (HFD), or HFD plus oral administration of abietic acid (20 mg/kg of body weight/day [LA] or 40 mg/kg of body weight/day [HA]) for 8 weeks. Compared with the HFD group, mice orally administered 40 mg of abietic acid/kg of body weight/day exhibited significantly decreased body weight and adipose tissue weights. Serum triglyceride concentrations in the HA group were significantly lower than those in the HFD group, as were the levels of serum insulin and leptin. Hematoxylin and eosin staining revealed that epididymal adipose tissue mass was decreased by abietic acid administration. Abietic acid also inhibited the protein expression of sterol regulatory element-binding protein-1c, CCAAT/enhancer-binding protein α, and CD36 in epididymal adipose tissues, which are up-regulated by HFDs. These data demonstrate that abietic acid has an anti-obesity effect in mice mediated by the regulation of adipogenesis.