The biological activity of fruiting bodies of cultured Cordyceps militaris C19 was examined and the antioxidant activity of the extract from Cordyceps militaris was investigated by using the chemical colorimetry. The experimental results showed that the extract from C19 fruiting bodies of cultured Cordyceps militaris had potent reducing power. When the concentration of the extract was 0.12%, its scavenging effect on DPPH· reached (49.74±1.83)%, and its inhibitory effect on the generation of MDA was (88.67±2.59)%. When the concentration of the extract was 0.6%, its scavenging effect on O2-· reached (83.22±3.07)%. And its scavenging effect on ·OH reached (69.59±2.24)% with its concentration being of 1%. It was indicated that the C19 fruiting bodies of cultured Cordyceps militaris was a potential natural antioxidant.