Seasonal variations in the environment (e.g. of temperature and light intensity) can lead to the excess production of reactive oxygen species and oxidative stress, inducing changes in the permeability of the plant cell membrane and the structure and function of cellular molecules. To address these deleterious effects, plants activate various non-enzymatic and enzymatic antioxidants. This study seeks to detect the influence of seasonal variation in Hedera helix (ivy) leaves, collected in Banj brdo (Banja Luka, Republika Srpska, Bosnia and Herzegovina) between December 2017 and November 2018, on oxidative (hydrogen peroxide and malondialdehyde) and antioxidant (superoxide dismutase, catalase, Class III peroxidases, and phenolic compounds) parameters. During the winter-early spring months (a temperature range of 0.7 to 5.4?C), we detected an increase in the values of all the oxidative and antioxidant parameters, whereas during the spring, summer, and autumn months (a temperature range of 15 to 25?C), the values of most of these parameters fell. However, a peak in the parameter values was detected during June and July 2018, which might be attributable to the influence of the changes in both light intensity and temperature and to the effects of intensive shoot growth. Our results highlight the importance of the antioxidant protection system of H. helix for its acclimation to seasonal variations in the environment, especially temperature.