Objective:To study the effects of 17-? estradiol on capillary ultrastructure of medulla oblongata in ovariectomized rats. Methods: The 30 adult femal rats were randomly divided into ovariectomy group(A group), estradiol group(B group) and sham- ovariectomy group(C group).The rats of A group and B group were bilaterally ovariectomized ,Which were injected with normalsaline 0.1 ml/d), 17-? estradiol(20 ?g/kg?d -1) ,The rats of D group were sham- ovariectomy ,animals were injected with normalsaline(0.1 ml/d), for 6 weeks. Results:(1)The level of serum estradiol of A group was significantly decreased compared with C group(P