We found previously that dietary high fat caused obesity, and levan supplementation to the regular diet reduced adiposity and serum lipids. In the present study, we examined the effects of levan [high-molecular-mass $eta$-(2,6)-linked fructose polymer] supplement on the development of obesity and lipid metabolism in rats fed with high-fat diet. Thus, to determine whether the dietary levan may have the anti-obesity and hypolipidemic effects, 4-wk-old Sprague Dawley male rats were fed with high-fat diet for 6 wk to induce obesity, and subsequently fed with 0, 1, 5, or 10% levan supplemented high-fat diets (w/w) for another 4 wk. For the comparison, a normal control group was fed with AIN-76A diet. Supplementation with levan resulted in a significant reduction of high-fat-induced body weight gain, white fat (i.e., epididymal, visceral, and peritoneal fat) development, adipocyte hypertrophy, and the development of hyperinsulinemia and hyperlipidemia in a dose-dependent manner. Serum triglyceride and free fatty acid levels were greatly reduced by levan supplementation. Serum total cholesterol level was reduced, whereas the HDL cholesterol level was increased by dietary levan. The expression of uncoupling protein (UCP) was increased by dietary high fat, and was further induced by levan supplementation. The mRNA level of UCP1, 2, and 3 in brown adipose tissue (BAT) and UCP3 in skeletal muscle was upregulated in rats fed with dietary levan. In conclusion, upregulated UCP mRNA expression may contribute to suppression of development of obesity through increased energy expenditure. The present results suggest that levan supplementation to the diet is beneficial in suppressing diet-induced obesity and hyperlipidemia.