Objective To investigate a possible role of orexin in the regulation of estrous cycle by examining the expression of orexin and orexin receptors(OX1R,OX2R) in the rat hypothalamus during the estrous cycle. Methods The levels of prepro-orexin(prepro-OX),orexin-A,OX1R,and OX2R in the rat hypothalamus during the estrous cycle were evaluated by competitive reverse transcription-polymerase china reaction (RT-PCR) assay. Results Only expression OX1R mRNA during late proestrus was significantly higher than that at metestrus.No significant changes of prepro-OX and OX2R mRNA expression were observed during the various estrous cycle phases.Conclusion Orexin might regulate the secretion of GnRH and/or LH by binding OX1R, contributing to the occurrence of ovulation.