Abstract: AIM　To observe the effects of estradiol benzoate on synaptophysin(Syn), parvalbumin(PV) and calbindin D28k(CaBP) immunoreactivity in hippocampus of ovariectomized(OVX) rats. METHODS　An animal model was developed using ovariectomized(OVX) rats, and immunoreactive technique was used with the help of an image analysis system. RESULTS　OVX in rats caused a decline in both integral optical density and area density of Syn, PV and CaBP immunoreactivity in hippocampus CA1 and dentate gyrus. These effects can be reversed by estradiol benzoate given 200 μg per rat, im, once every three days, for five weeks. CONCLUSION　The increase of expression of the synaptic protein and neuronal calcium binding capacity might be related to both the improvement of memory/learning behavior and the maintenance of neuronal calcium homeostasis.