In this study, the effect of Curcuma longa L. on obesity and insulin resistance was investigated in animals fed a moderate high fat diet. The animals used in this study were normal weight Spargue-Dawley (SD) rats and type 2 diabetic obese db/db mice. Accumulation of abdominal adipose tissue and weight gain were inhibited in the animals fed the C. longa extract. C. longa decreased fasting insulin and HOMA-IR in the SD rats, and effectively decreased blood glucose and hemoglobin A1c in db/db mice. C. longa decreased serum free fatty acid (FFA) level in the SD rats. FFA in db/db mice fed C. longa tended to decrease. C. longa significantly decreased serum triglyceride level. Our results collectively represent that C. longa prevented fat accumulation and insulin resistance in both normal weight SD rats and type 2 diabetic obese db/db mice fed a moderate high fat diet.