Abstract: Astaxanthin is an oxidized carotenoid,which mainly comes from microorganisms and marine organisms. Astaxanthin has strong antioxidant activity because of its special chemical structure. So it is widely used in health food,medical hygiene and other fields. In the paper,the antioxidation mechanism of astaxanthin is expounded from five aspects:Scavenging free radical,limiting oxidant permeating into cells,increasing antioxidant enzyme activity,reducing oxidative damage of DNA,inhibiting lipid peroxidation. The antioxidant ability of astaxanthin is discussed in three aspects:Scavenging free radical activity in vitro,inhibiting lipid oxidative degradation in oil system,astaxanthin inhibiting prooxidase,enhancing antioxidant enzyme activity. The comparison of antioxidation ability of astaxanthin with other natural astaxanthin such as lycopene,lutein,β-carotene,vitamin C and vitamin E are also reviewed in order to provide a reference for further study of astaxanthin antioxidant activity.