Crude extracts were prepared from fruiting bodies and mycelia of the medicinal fungus Cordyceps militaris, and a polysaccharide-enriched fraction was obtained after extraction with hot water and ethanol precipitation. Polysaccharide-enriched fractions were similarly prepared from Cordyceps sinensis, Omphalia lapidescens, and Tricholoma mongolicum. The various aforementioned preparations were orally administered into different groups of adult rats 24 h before an intraperitoneal injection of streptozotocin (40 mg/kg body weight), and subsequently daily for another 4 days. The dosage used was 10 mg/kg body weight for polysaccharide-enriched preparations and 100 mg/kg body weight for crude extracts. Control rats received distilled water instead of crude extract or polysaccharide-enriched preparation. It was found in the control rats that plasma glucose level rose from about 90 mg/dl before streptozotocin injection to levels that were maintained at about 300 mg/dl postinjection. All preparations produced hypoglycemic effects. C. militaris polysaccharide-enriched fraction displayed a more prominent effect than that of C. sinensis polysaccharide-enriched fraction which in turn was more potent than that of O. lapidescens and T. mongolicum polysaccharide-enriched fractions. The hypoglycemic effect of C. militaris polysaccharide-enriched fraction was dose-dependent.