β-defensin is widely detected in female reproductive tracts and is regarded to play an important role in the immune defence.This study aimed to investigate the regulation of β-defensin mRNA expression by progesterone in female reproductive tract. The epithelial cells of the Fallopian tube of Mongolian sheep was cultured in vitro. Cells were treated with different concentrations of progesterone (10^-6 ,10^-7 ,10^-8 ,10^-9 and 10^-10 mol/L) with or without mifepristone (the antagonist of progesterone),total RNA was extracted from cells,and the relative expression of β-defensin mRNA was detected using real time RT-PCR.The results showed that different concentrations of progesterone variously enhanced the expression of β-defensin mRNA in the epithelial cells of the Fallopian tube,while mifepristone significantly inhibited the expression of β-defensin mRNA induced by progesterone.These results illuminate that progesterone promotes the expression of β-defensin and that progesterone may affect the autoimmunity of the female animals via β-defensin pathway.