The tolerance of Elytrigia repens (L.) ‘Nevski’ to cadmium and the role of individual components of the antioxidant system (AOS) in the plants’ adaptation to elevated metal concentrations in the root layer were studied in a greenhouse experiment. Couch grass is highly resistant to cadmium and can for a long time (40 days) successfully grow in the presence of this metal at a 40 mg/kg concentration in the substrate while maintaining a high level of photosynthesis and water regime. It follows from these data that the high resistance of E. repens to cadmium, along with other protective mechanisms, is ensured by effective operation of the AOS. In particular, the activity of antioxidant enzymes suchas superoxide dismutase (SOD), catalase (CAT) and peroxidase (PO) in roots is significantly promoted in the presence of the metal. In leaves, only PO activity is promoted, but at the same time the synthesis of the AOS key non-enzymatic component, glutathione (GSH), becomes more active. Another contributing factor is the maintenance of a high concentration of carotenoids, which represent another group of non-enzymatic antioxidants. Based on the analysis of the results it was concluded that detoxification of reactive oxygen species in the plants’ roots, where a higher concentration of the metal was found, was mainly facilitated by enhanced activity of antioxidant enzymes, whereas in leaves the principal role in the prevention of oxidative stress under cadmium impact belonged to non-enzymatic low molecular weight compounds, in particular GSH and carotenoids.