Abstract: Investigation was made of effect of simulated Cd ²⁺ pollution on the antioxidase system and ultrastructure of the cells of Ottelia alismoides(L.)Pers.leaves,mainly chloroplasts,mitochondria and cell nucleus. It was found that with increase in the stress,superoxide dismutase(SOD)activity and soluble protein content decreased drastically,while malonyl(MDA)increased;and that the activity of peroxidase(POD)and catalase(CAT)peaked at 0 1mg/L of the pollutant and declined afterwards. Electronic microscopic observation showed that at the early stage of the toxication,chloroplasts and mitochondria were swelling up;and thylakoids vacuolized apparently. Higher concentration of Cd ²⁺ aggravated the damage,making chloroplast membranes disappear and chloroplasts disintegrate,mitochondrion mesenchyme dissolve and mitochondria be on the verge of disorganization,and nucleolus chromatin agglutinate and merge into cytoplasm. Cd ²⁺ pollution not only destroys the plant’s antioxidase system,but also causes irreversible damage to its ultrastructure,thus leading the cells to death.