This study was designed to investigate the expression of ghrelin mRNA in the hypothalamus of rats at the estrus and diestrus.Twelve virginal rats were classified into 2 groups as the estrus(n=6) and diestrus(n=6) which were determined by vaginal smears daily.All animals were killed by decapitation,and samples of hypothalamic tissue were obtained to detect the value of ghrelin and GnRH mRNA by real-time RT-PCR.Results showed that expression of ghrelin mRNA in the hypothalamus changed with the oestrous cycle,higher in the diestrus compared to that in the estrus(P<0.01),while on the contrary GnRH mRNA level was higher in the estrus than that in the diestrus(P<0.01).Results suggest that ghrelin may down-regulate the expression of GnRH mRNA in the hypothalamus.