Abstract: The effects of the heavy metal cadmium (Cd+2) on growth and activities of the antioxidant enzymes, catalase (CAT), peroxidase (POD) and polyphenol oxidase (PPO) have been investigated in Arabidopsis thaliana L. seedlings. The concentration of 50 and 100 μM CdCl2 was shown to strongly inhibit the growth of roots and lipid peroxidation. Lipid peroxidation of seedlings shoots rose with increasing concentrations of Cd+2 as indicated by malondialdehyde (MDA) concentration. As Cd+2 concentration increased, catalase (CAT) activity declined progressively, while peroxidase and polyphenol oxidase activity increased when compared to the untreated plants. Close correlations between increased MDA formation and decreased root growth as well as CAT activity suggests that lipid peroxidation might caused cell damage and death proposing that applied concentrations of Cd+2 could be toxic to cells. It was also noted that Cd+2-induced cell injury and lipid peroxidation correlated with increased peroxidase and polyphenol oxidase activities, two antioxidant enzymes involved in polyphenol peroxidation as lignification substrates. Together, the results suggest that in Arabidopsis thaliana reactive oxygen species (ROS) could be induced by phytotoxic concentrations of Cd+2 leading to increased POD and PPO activities which play a crucial role in detoxification of elevated concentrations of Cd+2 possibly via lignifications and physical barrier formation.