Abstract: In order to study the effects of estrogen on development and apoptosis of the pituitary cells， immunohistochemical SP method was used to detect the expressions of Bcl-2 and Bax in pituitary of rat that ovariectomized and treated with 17-β estrogen in different periods. The results showed that the expressions of Bcl-2 and Bax of the group sham operated (SHAM) in different periods had no remarkable change (P>0.05). The group ovariectomized (OVX) had significantly difference with the group SHAM and the group ovariectomized and treated with 17-β-E2 (OVX+E2)within the same stage (P<0.05). The expression of Bcl-2 in the sixth week after injection had a little increase than that before， and the Bax decreased. In terms of the eighth week， no remarkable difference was observed with the sixth (P>0.05). The results indicated that estrogen had certain regulative effect on the structure maintaining and function educing in pituitary.