Anti-obesity effects of Eriobotrya japonica leaf extracts were evaluated in 3T3-L1 adipocytes and ob/ob mice. Extracts of E. japonica were prepared with various solvents such as 80% methanol (MeOH), 50% ethanol (EtOH), and water using fresh or processed leaves. 80% MeOH, 50% EtOH, and processed water extracts of E. japonica leaves effectively inhibited lipid accumulation and expression of adipogenic transcription factors, peroxisome proliferator-activated receptor (PPAR)${gamma}$ and CCAAP/enhancer-binding protein (C/EBP)${alpha}$ in 3T3-L1 adipocytes. Oral treatment with 50% EtOH extract of E. japonica at 200 or 400 mg/kg body weight for 12 weeks significantly reduced the body weight and plasma triglyceride level compared to those of control group, ob/ob mice. Food efficiency ratio (FER) was significantly suppressed after treatment with E. japonica processed water extract in ob/ob mice. The plasma protein level of adiponentin was highly increased by feeding of 400 mg/kg body weight of 50% EtOH extract of E. japonica to ob/ob mice. Thus, these results suggest that the 50% EtOH extract of E. japonica has an anti-obesity effect through regulation of adipogenic transcription factors, and plasma lipid and adiponectin levels in 3T3-L1 adipocytes and ob/ob mice.