This study was conducted to investigate whether the obesity of obese fa/fa male Zucker rats can be ameliorated by mulberry leaves. There was no significant difference between mulberry treatment group and control group in body weight gain and food efficiency ratio. It also showed decreases on plasma triglyceride and total-cholesterol concentration compared to the control group. But there was no change in plasma leptin concentration between the control and mulberry treatment groups. These results suggest that mulberry leaves reduce serum lipid levels, but do not effect the plasma leptin concentration.