A hydroponic experiment was carried out in a greenhouse to study genotypic differences in the effect of four Cd levels on lipid peroxidation and activities of antioxidant enzymes in barley plants during ontogenesis. A highly significant increase in malondialdehyde (MDA) content, and a stimulation of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were recorded in plants subjected to 1 and 5μM Cd. The effects increased with both Cd concentration in the medium and with time of exposure in 5μM Cd treatments. There was a highly significant difference in the alternation of all these parameters but CAT activity among the four genotypes. Wumaoliuling, which was relatively sensitive to Cd toxicity in terms of growth, biomass and chlorophyll content both in the previous and present studies, accumulated much more MDA when exposed to 5μM Cd than the three other relatively tolerant genotypes (Zhenong 1, ZAU 3 and Mimai 114). In contrast, the three tolerant genotypes maintained higher SOD and POD activities than Wumaoliuling over the whole duration of Cd exposure. The present investigation showed that Cdstress induced a concentration-and genotype-dependent oxidative stress response in barley leaves, characterized by an accumulation of MDA and the alternation pattern of antioxidative enzymes, mainly SOD and POD may be attributed to the genotypic difference in Cd tolerance.