Under the conditions of a growing experiment, the authors studied the effect of zinc at concentrations of 5 (control), 50, 100, and 150 mg/kg substrate on growth, the intensity of lipid peroxidation (LPO), and the activity of the components of the antioxidant system in Brassica juncea L. (Сzern.) variety Slavyanka and Sinapis alba L. cultivar Belgium plants. Some differences and similarities were found in the AOS response of the studied species to an excess of zinc in the root environment. Thus, there were no changes in the intensity of lipid peroxidation in B. juncea under the influence of zinc in high concentrations, despite the high content of the metal in the roots and shoots. At the same time, even in the presence of metal at a concentration of 50 mg/kg substrate, an increase in the activity of guaiacol peroxidase (GPX) and catalase was observed. In S. alba at high concentrations of zinc in the substrate, the metal content in the shoots was higher than in B. juncea. At the same time, the content of malondialdehyde noticeably increased, despite the increased activity of superoxide dismutase and GPX. In both studied plant species, an increase in the zinc concentration in the substrate to 50 mg/kg and above led to an increase in the level of proline, while the content of carotenoids decreased. Considering that, in the studied concentrations, the metal had a less strong negative effect on shoot growth in B. juncea compared with S. alba, it was concluded that plants of this species are more resistant to excess zinc in the root environment.