Antioxidant and estrogenic effects of formononetin on ovariectomized mice have been investigated in the present study. The adult female Kunming mice were divided into 5 groups: sham-operated group, ovariectomized group, stilbestrol replacement therapy group (0.20 mg/kg day), low-dose formononetin group (0.05 g/kg day) and high-dose formononetin group (0.5 g/kg day). The mice in the latter 4 groups were ovariectomized. The drug was given by oral administration for 6 months. Estrogenic effect was determined by the change of uterine weight, and oxidant effects were determined by the content of SOD, GSH-Px, CAT and MDA. The intake of formononetin increased the uterine weight of the mice significantly as well as the content of SOD, GSH-Px, CAT, and reduced MDA in body. Formononetin had obvious antioxidant effects and estrogenic effect, and the estrogenic effect was not dosage-related.