In order to study the effect of ovariectomy on mechanical strength of vertebrae, 64 3-month-old female SD rats, weighing 180200g were divided into two payes for performing ovariectomy (OVX) and sham-operated(Sham-O), respectivly. The rats were sacrificed at 1,3,5,7 months later. Andanother group of 48 3 -month bipedal rats also renderment OVX and Sham-0 'operation and sacrificed at 2,5,7th month later. All L2 vertebra were measured morphogeometrically and then vertical compression test was caried. The results showed: in OVX rats, the average height of vertebrag became shortened(P<0.05), and the upper sagittal diameter become bigger(P<0.05). In abnormal high mechanical stress OVX rats, the average height of vertebrae became shorte-n(P<0.05), and both the upper and lower arrow diameter became bigger(P<0.05). The mechanical strength declined from 1st month and continued to the lowest at 7th month. Also the mechanical strength showed decline change but less than normal OVX group. Such alterations in bipedal rats may be related to the high mechanical stress in vertebrae. The mechanical strength is so low that the fracture risk is higher even in case of a slight trauma.