This experiment was carried out to investigate the effects of unilateral and bilateral ovariectomy in immature rats on the weight of body, ovary, uterus and adrenal gland and the change of serum FSH and LH level. Ninty Sprague-Dawley female rats, 23${pm}$2 days old, were divided into 3 groups with 30 heads per group; control, unilaterally and bilaterally ovariectomized group. Each group was subdivided into 6 groups according to 6 experimental periods; day 4, 8, 12, 16, 20, and 24 after operation. Five rats at every 4 days intervals were measured their body weights and sacrificed for the measurement of their ovarian, uterine and adrenal weights and at the same time blood samples were taken for the determination of serum FSH and LH level by radioimmunoassay. The following results were obtained: 1. Body weights in the unilaterally and bilaterally ovariectomized goups were higher than those of control groups during all experimental periods, even though there were no significant differences among the above 3 groups. 2. A significant hypertrophy of the remained ovary in the unilaterally ovariecto mized group was observed from day 16 till day 24 after operation. The ovarian weight; 22.1${pm}$1.73mg, at day 16 in control group was smaller than the unilaterally ovariectomized group weighing 50.5${pm}$8.45mg (p<0.01) and the ovarian weights, 75.9${pm}$2.25mg and 63.3${pm}$7.08mg ; at day 20 and 24 in unilaterally ovariectomized group were significantly larger than 29.1${pm}$2.33mg and 26.3${pm}$1.76mg in control group, respectively (p<0.01 and p<0.05). 3. The uterus of bilaterally ovariectomized group were remarkably atrophied from day 8 after operation as compared with those of control and unilaterally ovariectomized group. The uterine weight at day 24 was 96.7${pm}$9.15mg for control group, 139.4${pm}$1.73mg for unilaterally ovariectomized group and 21.7${pm}$1.08mg for bilaterally ovariectomized group, respectively and there were significant differences among 3 groups (p<0.01). 4. A statistically significant increase ofthe weight of adrenal gland was observed at day 16 in the unilaterally ovariectomized group with 24.4${pm}$2.58mg against 15.5${pm}$3.09mg in control group and 13.9${pm}$1.38mg in bilaterally ovariectomized group (p<0.05). The adrenal gland weight in unilaterally ovariectomized group with 24.7${pm}$1.63mg at day 20 and 31.2${pm}$1.62mg at day 24 increased significantly as compared with bilaterally ovariectomized group with 15.1${pm}$13.11mg at day 20 and 15.6${pm}$1.76mg at day 24. 5. Serum FSH level of unilaterally ovariectomized group increased remarkably up to 2.97${pm}$0.37mIU/ml at day 4 after operaton and then decreased gradually. Serum FSH level of bilaterally ovariectomized group were higher than those of control group throughout all experimental periods. 6. Serum LH level ofunitelarally ovariectomized group with 3.17${pm}$0.32mIU/iml at day 4 and 3.57${pm}$0.58mIU/ml at day 24 increased noticeably more than those of control group with 1.79${pm}$0.16 mIU/ml at day 4 and 2.17${pm}$0.27mIU/ml at day 24 (p<0.05).