The present study was carried out to evaluate the physiological effects of mushroom supplementation on blood glucose levels, lipid profile, and antioxidant enzyme activities in subjects with type 2 diabetes mellitus. Subjects were randomized into either a control group or mushroom supplementation group. Mushroom supplementation was provided 3 times a day for 4 weeks. We found that total dietary fiber intake was about 2.5 times higher (30.3 g vs. 12.3 g) in subjects receiving mushroom supplementation than in the control group. Two groups maintained the same food intake and amount of activity, exercise during the supplementation. We observed no difference in age, height, weight, BMI (body mass index), blood pressure between the groups. Nutrient intake did not differ appreciably between the two groups, except for fiber intake, during the supplementation. Fasting blood glucose levels and 2-hour postprandial blood glucose levels were significantly lower in those ingesting mushroom than in controls. Furthermore, the concentrations of low-density lipoprotein cholesterol were decreased significantly in the mushroom supplementation group. Small changes were observed in the concentration of total cholesterol, triglyceride, high-density lipoprotein cholesterol of those supplemented with mushroom, but these changes were not statistically significant. Activities of superoxide dismutase and catalase with mushroom supplementation were higher than in controls, but and glutathione peroxidase activity was not affected. The levels of thiobarbituric acid reactive substance of mushroom group were lower than control group, but were not significant. We conclude that addition of mushroom influences glycemic control and may be effective in lowering blood lipids and improving antioxidant enzyme activities. Accordingly, such effects may reduce risk factors for cardiovascular disease in patients with type 2 diabetes. However, to confirm these effects and to make dietary recommendations for patients with type 2 diabetes, further studies are necessary.