Objective: To explore the effect of melatonin and melatonin receptors on the onset of the puberty by observing the plasma concentration of melatonin and melatonin receptors (MT1,MT2)of hypothalamus and pituitary in precocious puberty female rats. Methods:A total of 40 26-day-old female SD rats were divided into the precocious puberty group(A),the treated group(B)and the control groups including the prepuberty group(C1)and the normal puberty group(C2). N-methyl-DL-aspartic acid(NMA)was used to establish precocious puberty female rat model. GnRH analog(Triptorelin) were used to treat precocious puberty. The nocturnal plasma melatonin and luteinizing hormone(LH) level were assayed by enzyme linked immunosorbent assay(ELISA)and the expressions of melatonin receptors(MT1,MT2) and GnRH mRNA were conducted in hypothalamus and pituitary by real time-PCR. Results:There was no significant difference in the plasma melatonin level in each group. The expression of MT1 mRNA of rat hypothalamus and pituitary in the group A was significantly lower than in the group B and C1,and similar with the group C2. Each group showed no significant differences in the expressions of MT2 of hypothalamus and pituitary. Conclusion:The expressions of MT1 mRNA decreased in precocious puberty female rats. GnRH analog may upregulate the expression of MT1 mRNA in hypothalamus and pituitary. The inhibitory effects of melatonin may decline due to the decreased expression of melatonin receptors in the central nervous system by decrease the expression of melatonin receptor in the hypothalamus. Melatonin and its receptors may participate in normal puberty or precocious puberty.