Astaxanthin is a high-value carotenoid (3, 3' dihydroxy-beta carotene-4, 4'-dione) with multiple biological properties of interest. It is produced by a microalga, Heamatococcus pluvialis, in substantial amounts especially under stressful conditions such as nitrate starvation and high-light intensity. The present study investigated the gastric ulcer prevention, harmlessness, and antioxidant activity of dimethyl sulfoxide-extracted (DMSO) astaxanthin (DMSO-AE) of a newly isolated Haematococcus pluvialis Algerian strain. The experiment was carried out using the ethanol-induced gastric ulcer model in mice. Changes in behavior, physical appearance, convulsion, and death rate were regularly monitored during the first 3h and after the next 24h. Antioxidant activity of H. pluvialis DMSO-AE was evaluated with DPPH (2, 2'diphenylpicrylhydrazyl) method. Ethanol-induced gastric ulcer was significantly (P<0.05) reduced in mice treated with 250 and 500 mu g of H. pluvialis DMSO-AE/Kg BW, when compared to the negative and the positive control groups. Histopathological examination of stomach sagittal sections of H. pluvialis DMSO-AE pretreated mice did not show any modification of tissue architecture. There was no evidence of toxicity or changes in the behavior or the mortality rate of the mice at the administrated dose of 500 mg H. pluvialis DMSO-AE/Kg BW. The DPPH scavenging activity of H. pluvialis DMSO-AE used at a concentration of 200 mu g/mL, was about 89.97% with an IC50 value of 25.82 mu g/mL. These results highlighted the astaxanthin protective effects on ethanol-induced gastric ulcers and lipid peroxidation which open up the prospects for the use of this carotenoid in the food, pharmaceutical, and cosmetic industry.