Pregnancy is attended by the raised risk of oxidative stress. Pregnant organism could also get different stress situations, for example, hypoxia. We studied the influence of pregnancy (period of early organogenesis) and acute hypobaric hypoxia (AHH) on rats' antioxidant system (AOS). In experimental groups non-pregnant rats and rats on the 9–10th day of pregnancy were subjected to AHH in a pressure chamber (oxygen pressure corresponded to 11 500 meters above sea-level). Impact lasted before stop of rat's breath, but no more, than 10 min. Each experimental group had own control not subjected to AHH. Superoxide dismutase activity (SOD, one of the most important enzymes of AOS) and concentration of substance reacted with tiobarbiturate acid (TBA-active products, the markers of oxidative stress), determined 24 h after stress in the blood plasma by spectrophotometric analysis were the criteria of AOS-work. Control pregnant females showed 32.92.6% higher SOD-activity and the same concentration of TBA-active products than control non-pregnant females. Thereby pregnancy mobilizes AOS-system. This mobilization could be the cause of unchanged level of oxidative stress markers. Pregnant rats after AHH had 13.04.0% higher SOD-activity and 11.14.2% more TBA-active products, than control pregnant rats. The non-pregnant females from experimental and control groups had no differences from each other. We therefore can conclude that AHH has more prolonged consequences for AOS and oxidative status of pregnant rats than non-pregnant.