Sagittaria sagittifolia L. was cultivated in Cd²⁺ and Cr⁶⁺ solution, imitating polluted water environment,the toxic effects of the two single ions on the physiology and biochemistry in roots and leaves of Sagittaria.sagittififolia L. were measured. It's found that the chlorophyll content and the relative membrane penetrability(RMP) of root cells increased first and decreased afterwords with the augmenting of Cd²⁺ and Cr⁶⁺ concentration in the solution;With Cd²⁺ concentration augmenting, peroxidase(POD) activity in roots and leaves, superoxide dismutase (SOD) activity in leaves, malondiadehyde(MDA) content and the generation rate of superoxide anion(O₂^-) in roots all increased first and decreased afterwards;And catalase(CAT) activity in roots and leaves, SOD activity in roots, MDA content and the generation rate of O₂^- in leaves were all increased gradually. For the plants treated only with Cr⁶⁺, the content of MDA and the activities of SOD, CAT and POD in roots increased with the augmenting of concentration, but the generation rate of O₂^- and the activities of SOD, CAT and POD in leaves increased first and decreased afterwards;Both Cd²⁺ and Cr⁶⁺ destroyed S..sagittifolia L. in the polluted solution, and the toxic effects were either same or different. The toxic effect on roots was more severe than that on leaves under the equal concentration of Cd²⁺ and Cr⁶⁺.