Nutritional characteristics of buckwheat flour and fiber were studied for their effects on obesity and metabolic parameters in mice. Three types of diet with differing fiber content were used for the study. The Gozenko diet consisted of buckwheat flour with 3.3 wt% fiber. The lzumo Soba diet consisted of buckwheat flour with chaff and contained 6.0 wt% fiber. The third dict was the Cornstarch diet, consisting of cornstarch flour with 3.1 wt% fiber. After the mice were fed their respective diets with equal calorie for 30 days (16.6 kcal / day / mouse), the liver weight of the lzumo Soba diet group was significantly less than that of the Cornstarch or Gozenko diet groups. Additionally, the Cornstarch and the Gozenko diet groups had higher values for liver triglyceride contents than did the lzumo Soba diet group. Plasma y-GTP and GPT for the lzumo Soba diet group were significantly lower than those for the Cornstarch diet groups, and GOT for lzumo Soba diet group was significantly lower than that for the Cornstarch or Gozenko diet groups. We concluded that the lzumo Soba diet, containing large amount of dietary fiber from the buckwheat chaff, has the potential for preventing liver steatosis.