Genetically diabetic (type II) KK-Ay mice, male and 5 wk of age, were divided into four groups and fed test diets containing 2(2F). 5(5F). 10(10F), or 20(20F)% fat for 4 wk. and then the 5F group and one-half of the 20F group continued to be fed the corresponding diet and the other half of the latter group was given the 20F (20FHWE) diet with 5% hot-water extracts (HWE) from woody ear (Auricularia auricula-judae Quel.) for a further 3 wk. Remarkable changes in body weight were unfound among the dietary groups. The food intake generally decreased according to the increase in dietary fat content, but the energy expenditure was hardly different among the dietary groups except for the 20FHWE group. That of the 20FHWE group was further decreased compared to the 20F group. Water consumption dropped in the order of the 20F. 5F, and 20FHWE groups. The plasma glucose concentration was the highest in the 20F group, followed in order by the 10F and 5F groups, and the lowest in the 2F and 20FHWE groups. The contents of dietary fat were most positively correlated with the plasma glucose level. The present results using KK-Ay mice confirm that dietary fat levels control postprandial glycaemia. and suggest that the hypoglycemic effect of HWE is primarily caused by a reduction in food ingestion.