An influence of 10-(6'-plastoquinonyl)decyltriphenylphosphonium (SkQ1) on oxidative status and activity of some antioxidant enzymes in the liver and blood serum from rats was examined during experimental hyperglycemia developed after injecting protamine sulfate. It was found that SkQ1 lowered glycemic level in rats treated with protamine sulfate. Moreover, it was also accompanied by restoration of the normal range of biochemiluminescence parameters indicating the rate of ongoing free radical processes, magnitude of primary products of lipid peroxidation such as diene conjugates, activity of aconitate hydratase, and level of citrate in rat liver and blood. Hence, it was demonstrated that activity of superoxide dismutase and catalase, increasing during hyperglycemia, was decreased after administering SkQ1. This might be related to the ability of SkQ1 to normalize free-radical homeostasis imbalanced during hyperglycemia.