Our previous study demonstrated that the fruiting bodies of Cordyceps sinensis, a traditional Chinese medicine, attenuated diabetes-induced weight loss, polydipsia, and hyperglycemia in rats. In the present study, we further compared the anti-hyperglycemic activity of the fermented mycelia and broth of Cordyceps sinensis with that of the fruiting bodies. Male Wistar rats orally administered a placebo (STZ group), fruiting bodies (FB group, 1 g/day), fermented mycelia (MCS group, 1 g/day), fermented broth (BCS group, 1 g/day), or fermented mycelia plus broth (XCS group, 0.5 g/day of each) of Cordyceps sinensis (d1 to d28) were injected with nicotinamide (200 mg/kg) and streptozotocin (65 mg/kg) on d15. Rats fed with a placebo and injected with saline served as the control (CON) group. The amount of water and food consumption (d15 to d29), the 2-hour-postprandial blood glucose concentrations (d21 and d28), and the serum concentrations of fructosamine (d29) were significantly lower in the FB, MCS, BCS, and XCS groups than in the STZ group (one-way ANOVA, p < 0.05). The diabetic rats had significantly higher blood glucose concentrations as measured by the oral glucose tolerance test than the control rats; moreover, these changes were significantly reduced by ingesting the fruiting bodies, fermented mycelia and/or broth of Cordyceps sinensis. Our results revealed that the fermented mycelia and broth of Cordyceps sinensis have anti-hyperglycemic activities similar to those of the fruiting bodies. Therefore, the fermented products of Cordyceps sinensis could be developed as potential anti-diabetic agents or functional foods for persons with a high risk of diabetes mellitus.