Astaxanthin due to its strong antioxidant activity is believed to reduce oxidative stress and therefore is considered as feed additive in pathological conditions and also for the athletes. It is promoted by several equine web portals, however, data supporting that concept in horses is limited. Thus, the aim of this study was to evaluate the effect of astaxanthin supplementation on the parameters of oxidative status in 3 years old, racing Arabian horses during long term observation and the changes related to a single training session of high intensity. Six horses were supplemented with astaxanthin at a dose of 0.52-0.58 mg/kg BW and 7 received no supplementation. Astaxanthin supplementation resulted in the increase in total antioxidant status by 31.5%, accompanied by decreases in the amount of total thiobarbituric acid-reactive substances -TBARS and glutathione reductases - GR values by 34.5% and 45.4%, respectively, after 1 month and this effect persisted until the end of the observation. After individual training session the activities of glutathione peroxidases and GR were lower by 69% and 46%, respectively, and TBARS lower by 38% in supplemented horses. These results directly confirmed the beneficial effects of astaxanthin supplementation on the antioxidant status of race horses. Astaxanthin partially counterbalance the training-related oxidative stress, save the horse natural antioxidant defense, and shift the redox status towards a more reducing environment. At the same time, exercise-induced reactive oxygen species production at certain level was maintained and so that contributed to training progress.