Background: Progesterone produced by the corpus luteum (CL) is essential for preparation, implantation and maintenance of gestation. Furthermore, progesterone plays a protective role against luteolysis in rodents. It has been reported that Slit/Robo family members expressed in the CL and involved in prostaglandin F-2 alpha(PGF(2 alpha)) induced luteolysis. However, the interactions between progesterone and Slits/Robos in CL are not clear. This study was designed to examine whether or not luteolysis is regulated by the interaction of progesterone and Slits/Robos in mouse CL. Methods: In the current study, we used Real-time PCR to identify the effect of progesterone on Slit2/Robol expression in cultured luteal cells in vitro, and the exogenous progesterone injection on mouse luteolysis and Slit/Robo expression in vivo was studied via Real-time PCR and Western bolt. Results: Our in vitro experiment revealed that 1 mu M progesterone significantly decreased Slit2/Robol mRNA levels at 6 h, 12 h and 24 h. Our in vivo experiment showed that the mRNA and protein levels of Slit2 and Robol decreased significantly 7 days after progesterone supplement. Conclusion: These findings indicate that progesterone maintains CL function and resists luteolysis possibly through down-regulating Slit/Robo signaling pathway in the CL.