Abstract: 【Objective】 To analyze the effect of exogenous melatonin (MT) treatment during pregnancy on the growth of the female offspring in the rat. 【Methods】 A total of 30 Sprague-Dawley rats were randomly?dividedinto?three?groups and treated with melatonin (MT-LD group:10 mg?kg-1?d-1

MT-HD group: 40 mg?kg-1?d-1) from day 15 of pregnancy to the day of delivery. The control rats were treated with saline solution under the same conditions. Female offspring body weight were assessed every week. Age of vaginal opening and oestrouscyclicity were assessed to determine the timing of pubertal onset. Serum

femur

tibia samples were taken before the first estrus or diestrus after stabilizing of the sexual cycle among every group. FSH

LH

melatonin growth hormone (GH) levels were measured. 【Result】 In total

273 female offsprings were get

there were 92 rats in MT - LD group

84 rats in MT - HD group

and 97 rats in control group only. The body weight statistically increased in MT-HD group respect to the other two groups

and weight in MT-LD group were significantly heavier than that in the control group(P < 0.001). The offsprings of melatonin (40 mg?kg-1?d-1) treated rats (MT-HD group) showed earlier vaginal opening and the onset of first diestrus than the other two group(P < 0.001). However

no differences were detected between MT-LD group and control group. The concentrations of FSH

LH

melatonin

and GH were statistically increased in MT-HD group(P < 0.05). However

those variables were not significantly different between the MT-LD group and control group. 【Conclusion】 Mother’s melatonin treatment can affect weight

longitudinal bone growth and sexual maturation in developing rats. We should take into account these influences when melatonin treatment used in the pregnancy women.