Biochemical and histological alterations in erythrocytes, liver, kidney and brain of rats fed 30% level of D. juxtaposita fern powder were studied. Significant increase in GSH and decrease in lipid peroxidation, acetyl choline estrase and catalase of RBCs was observed. Significant increase in lipid peroxidation, ATPases and decrease in GST on 80 days post feeding in liver, kidneys and brain and acetyl choline estrase in brain was observed as compared to control. Histopathological studies indicated mild vascular changes in lungs, degenerative changes in testes, focal necrosis in liver and villous atrophy or hyperplasia of lining epithelial cells and hypersecretory activity in intestinal glands. Toxic effect of Dryopteris on rats was due to membrane alterations and oxidative stress and degenerative and vascular microscopic pathological changes.