Treatment of different concentrations of both hexavalent and trivalent chromium on Azolla pinnata resulted in significant biochemical and oxidative aberrations. Total peroxide increased, while lipid peroxidation decreased, as indicated by malondialdehyde formation after 48 h treatment. Ascorbate and glutathione contents increased under chromium treatment. Activity of catalase decreased whereas guaiacol peroxidase, glutathione reductase and superoxide dismutase activities increased along with the period of metal treatment. These results suggest that acute chromium toxicity induces oxidative damage in Azolla pinnata.