Objective: To evaluate effects of CordyMax(TM) Cs-4, a mycelial fermentation product of Cordy-ceps sinensis, on improving glucose metabolism and insulin sensitivity. Design: An in vivo pharmacology study. Subjects and Study Interventions: Adult Wistar rats, male and female, were given CordyMax 250 or 500 mg/kg per day or placebo for 17 days by gavage. Outcome Measurements: Fasting blood glucose, fasting plasma insulin, glucose-insulin index, and oral glucose tolerance. Results: Rats fed Cs-4 at either 250 or 500 mg/kg showed significantly reduced fasting blood glucose after the 17-day treatment, by 27% and 24% from baselines respectively (both p < 0.001). Examination of fasting plasma insulin demonstrated a 37% decrease in the high dose treatment groups (p = 0.012). Glucose-insulin index, an index of insulin sensitivity, increased by 10% and 17% in both 250 and 500 mg/kg groups (p = 0.008 and p = 0.0001, respectively). Oral glucose tolerance tests showed significantly improved glucose tolerance at 0.5, 1.0, and 2.0 hours after oral administration of a bolus of glucose (the area under the glucose curve: p = 0.05-0.006), but no change at 5 hours. Conclusion: CordyMax Cs-4 is effective in lowering basal blood glucose and plasma insulin, improving glucose metabolism by enhancing insulin sensitivity, and improving oral glucose tolerance.