The present study aimed to determine the adaptation capacity of horses subjected to defined, seasonally variable exercise on the basis of selected indicators of their oxidative status. The research was carried out over a two-year period on 25 Polish Noble Half-bred horses (PKSP). All horses came from stables in south-eastern Poland (51°15’00”N, 22°34’00”E) and competed in show jumping. According to the intensity of exercise, two experimental periods were distinguished, characterized by moderate intensity of exercise (D1) and high intensity of exercise (D2). The test material consisted of blood taken from the external jugular vein into dry tubes in a closed system. Samples were collected four times. The oxidative status was determined by means of PerOx reagents (TOS/TOC) and ImAnOx reagents (TAS/TAC) from Immundiagnostik. The results were analyzed statistically with the Statistica 10 software (StatSoft Inc.). Changes were found in all parameters studied. The average level of total antioxidant status (TAS) in our research was low, and the average level of total oxidant status (TOS) obtained in the experiment corresponds to a low level of oxidative stress. The oxidant status and the antioxidant status did not correlate with each other. The values were balanced regardless of sex or age, which suggests that training did not result in oxidative stress. Our results also suggest that evaluation of blood oxidative markers can help in assessing the welfare of training horses.