Sparassis crispa (SC), known as Hanabiratake in Japanese, is an edible mushroom with medicinal properties; however, its antidiabetic activity is not well established. In the present study, we examined the effects of dietary SC on diabetic mice. KK-Ay mice that were fed SC for 3 or 6 weeks showed pronounced increase of plasma levels of adiponectin. Significant decrease of blood glucose and insulin levels were also observed by 3 week-administration of SC. Moreover, mice that were fed the SC diet exhibited relatively decreased serum levels of triglycerides and total cholesterol. Although the SC diet had no effect on body and adipose tissue weights in KK-Ay mice, the size of the mesenteric adipose cells of SC group was smaller than control group though it was not significant difference. Thus, the SC diet might decrease the adipose cell size in order to increase plasma adiponectin levels. Considering the physiological significance of adiponectin in type 2 diabetes, insulin resistance, and cardiovascular diseases, these findings imply that dietary SC has the potential to ameliorate these diseases.