Haematococcus pluvialis, a green alga accumulates astaxathin upto 2-3% on dry weight basis. In the present study, identification of carotenoids from Haematococcus cyst cell extract by HPLC and LC-MS (APCI) and their antioxidant properties were evaluated in vitro model systems. The extract exhibited 89% and 78% antioxidant activity in beta-carotene linoleate model, and hydroxyl radical scavenging model at 9 ppm of total carotenoid respectively. The extract also showed 80%, 85% and 79% antioxidant activity against lipid peroxidation in kidney, brain and liver of rats. Low-density lipoprotein oxidation induced by Cu2+ ions also protected (45%, 64% and 75%) by the extract in a dose dependent manner with different carotenoid levels. Thiobarbituric acid reactive substances concentration in the blood, liver, and kidney of rat was also significantly (p<0.005) decreased in H. pluvialis treated rats. Potent antioxidant activity is attributable to various carotenoids present in the extract.