Investigating the antioxidant activities of water and ethanol extracts of natural Cordyceps sinensis and Cordyceps militaris and their fermentation preparations. The samples were tested through 6 assays: inhibition ability of linoleic acid oxidation; scavenging activity of DPPH, hydrogen peroxide, hydroxyl radical and superoxide anion; and metal chelating activity. Samples showed different antioxidant ability, and there was not an extract that exhibited high activity in all assays; however, water extract of natural C. militaris could be regarded as the most powerful antioxidant among 8 samples. It had high activity in inhibition of linoleic acid oxidation, chelating metal ions, and scavenging DPPH and hydroxyl radical. The research also indicated that the contents of phenolic compounds in water and ethanol extracts of natural and cultured Cordyceps sp. had huge difference. Natural Cordyceps sp. and its fermentation preparations could be used as potential natural antioxidants. The fermented process affected the antioxidant ability of cultured Cordyceps sp., and the antioxidant activity of both natural and cultured Cordyceps sp. did not significantly related with the quantity of phenolics.