Simple SummaryIntensive physical activity can cause some deleterious effects on athletes’ health and sports performance. One of the main reasons for these effects seems to be oxidative stress. Therefore, this study was conducted to see if supplementation with an enzymatic antioxidant containing superoxide dismutase of plant origin, GliSODin, could reduce some negative effects of oxidative stress connected to exhaustive exercise. According to the results of this study, it was concluded that supplementation with GliSODin can protect athletes from muscle damage and decrease inflammation caused by intensive physical activity and have some positive influence on the sports performance of elite rowers. Therefore, more studies with a larger number of participants are needed to confirm this positive effect of GliSODin supplementation.This study aimed to investigate the effect of supplementation with plant origin superoxide dismutase (SOD), GliSODin, on parameters of muscle damage, metabolic, and work performance at international level rowers. Twenty-eight rowers were included in a randomized, double-blind study. The study was conducted during a 6-week preparation period. At the beginning of the study and after 6 weeks of the supplementation period, all rowers were tested on a rowing ergometer. Blood samples were taken from the antecubital vein before and after every ergometer testing. Muscle damage markers creatine kinase (CK) and lactate dehydrogenase (LDH), total antioxidant capacity (TAC), inflammation parameters interleukin-6 (IL-6), and C-reactive protein (CRP) were measured. Rowing performance was assessed by lactate level in capillary blood and power output on the rowing ergometer. After supplementation, experimental group had significantly lower CK (p = 0.049) and IL-6 (p = 0.035) before and IL-6 (p = 0.050) after exhausting exercise on ergometer. Relative change of power output at 4 mmol/L concentration of lactate in blood, considering the initial and final test, was significantly higher (p = 0.020) in the supplemented group. It was concluded that GliSODin could be considered a good supplement in preventing some deleterious effects of intensive physical activity, including inflammation and muscle damage, and consequently, to enable a better rowing performance of elite rowers.