The Konjac flour (KF) was from Amorphallus Konjac, a kind of food, rich in dietary fibre composed mainly of gluco-mannan, but trace protein and very low energy.Male and female Spraue-Dawley rats aged 24 days were divided into 3 groups. All 3 groups were fed with high lipid and high nutrition diet. The group A was set as control, group B and group C plus KF in diet daily oral dose of 1.9mg/g and 19mg/g body weight respectively.After 45 days feeding, the following results were obtained;1. The increases of body weight in rats were reduced by oral KF.2. The size of fat cells in abdominal tissue and fat weight were greater in control group than in the other groups. These results suggest that KF has a significant effect on reducing obesity.3. No significant differences were found among the three groups in serum of chol, TG and some elements.4. The moist faeces in the KF groups were greater than the control group5. No side effects were found on the tests.