This experiment was conducted to investigate the effects of ovariectomy and estradiol benzoate administration on body growth and development of endocrine glands in female rats. One hundred and twenty female rats, 30 days old weighing 72.0${pm}$3.0g, were divided into control and ovariectomized groups and divided again into two groups, treated and untreated with estradiol benzoate, respectively. Each group was composed of 30 rats. Hormone was injected every two week interval. The body weight was measured weekly from the beginning of treatment to 63 days after treatment and 6 rats per group were sacrificed at 7, 21, 35, 49 and 63 days after treatment for weight change of endocrine gland. The results obtained were as follows: 1. the changes in the body weight during the experimental period were not signifilcantly different between two groups, although the body weight of ovariectomized groups were heavier than that of control groups and the body weight of treated group with estradiol benzoate was heavier than that of untreated group. 2. The body lengths in all groups were increased proportionally to body weight until 63 days after treatment and there were not significantly different among the experimental groups. 3. The weight of hypophysis treated with estradial benzoate in ovariectomized groups was continuously increased in the whole period and was highly significant at 49 and 63 days after treatment as compared with those of untreated in ovariectomized group. 4. Adrenal gland weights of the control and ovariectomized group treated with estradiol benzoate were distinctly light at 21 days after treatment, but there were not significantly different among all groups at 35 days. Adrenal gland weight of ovariectomized groups was smaller than control groups at 49 days and untreated group in ovariectomized groups was considerably smaller than the other 3 groups at 63 days after treatment. 5. In control rats, the ovary weight treated group with estradiol benzoate was larger than the untreated group at 35 days after treatment, but was smaller than the untreated group after 49 days. 6. The weight of reproductive tract in ovariectomized groups were markedly smaller than control groups till 35 days after treatment. The growth of reproductive tract untreated in ovariectomized groups was almost completely depressed.