Cadmium (Cd), known as a non-essential heavy metal, can cause oxidative stress in plants. In this study, an attempt was carried out to find out whether Cd-induced oxidative and microscopic changes could be observed in the early stage of seedling growth. Seeds of Brassica napus (cvs. Zheda 619 and ZS 758) were germinated in vitro at 0, 100, 200, 300, and 500 μM Cd concentrations in dark for 48 hours. Results showed that the higher concentration of Cd (500 μM) significantly reduced plant growth in both cultivars. However, Cd concentration in both cultivars increased linearly with the Cd concentration, but was more pronounced in ZS 758 than the other cultivar.Moreover, Cd caused oxidative stress in germinated seeds by increasing reactive oxygen species, however, no relationship was found between antioxidative defense capacity including catalase, peroxidase, superoxide dismutase and glutathione reductase activities and Cd tolerance in the two cultivars. Cd toxicity showed significant ultrastructural changes in germinated seed cells, but cell structure in Zheda 619 did not show any difference, while cell structure in ZS 758 was totally damaged under higher concentration of Cd (500 μM).Based on the present findings, it can be concluded that cultivar Zheda 619 showed comparatively higher tolerance and integrity of cell organelles under Cd stress.