Abstract Human activities are increased in Antarctica during decades, primarily due to the logistic and tourism operations, which consequent negative impact on penguin populations, altering their physiological responses. Therefore, we aimed to assess the blood biochemistry and oxidant/antioxidant balance of Adélie penguins (Pygoscelis adeliae) inhabiting two selected colonies: Potter Peninsula, considered as a low impacted colony, and Esperanza/Hope Bay as a high impacted colony. The levels of calcium, uric acid, and fructosamine, showed significant high values (p<0.05) for the Potter Peninsula´s penguins. Besides, this population showed high levels of plasma protein oxidation and erythrocyte lipid peroxidation (p<0.005) while the Esperanza/Hope Bay population presented high levels of erythrocyte protein oxidation and plasma lipid peroxidation (p<0.005). The oxidative damage values were similar in the Potter Peninsula population and slightly lower in the Esperanza/Hope Bay penguins if the results were compared to previous reports. The enzymes superoxide dismutase and glutathione peroxidase had significantly (p<0.005) high activity in the Esperanza/Hope Bay population, which also showed high reduced glutathione levels. The glutathione S-transferase activity was significantly high (p<0.005) in the Potter Peninsula population. The obtained results might take into account for making decisions about management and protection plans for the different penguin nesting areas in Antarctica.