OBJECTIVE: We inferred how KISS-1/GPR54 system to involved in precocious puberty by observing hormones level during the process of precocious puberty in model and normal rats during sexual development and the estrus cycle. METHOD: Female rats were divided randomly into CPP and control groups; the former were injected with NMDA twice daily, and control groups were injected with saline. Blood and tissue samples were collected and measured during the stages of prepuberty, vaginal opening, estrus, proestrus and diestrus. RESULTS: The times of onset of puberty and sexual maturity in the CPP group were significantly earlier than in the control groups. Hypothalamic levels of KISS-1 and GPR54 gene expression, kisspeptin, luteinizing hormone, and follicle stimulating hormone started to rise before puberty. In stable estrus cycles, kisspeptin levels were the lowest during proestrus, while gonadotropin-releasing hormone (GnRH) levels rose to the highest during estrus. GnRH levels increased significantly in the estrus cycle compared with the prepubertal stage, but kisspeptin levels did not change significantly. CONCLUSION: the hypothalamic KISS-1/GPR54 system might permit the onset of puberty, but is not its primary trigger. Hormone levels were lower and gonadal maturity markers in the CPP groups were worse than in the control groups.