Objective:To study the effect of YiKang decoction on expression of leukemia inhibitory factor(LIF) in human endometrium of unexplained infertile women, and explore the possible mechanism of YiKang decoction for infertily treatment. Methods:Twenty infertile patients were treated with standard dose of YiKang decoction for two months. LIF mRNA levels in the endometrium of late luteal period were detected by RT-PCR and Real-time quantitative PCR. The protein levels and expression sites of LIF were subsequently confirmed by Immunohistochemistry(IHC). Results:The real-time quantitative PCR Ct value for LIF mRNA before and after treatment were 9.79 ± 0.91 and 4.60 ± 1.24, respectively, suggesting that the transcription level of LIF was higher after treatment(P < 0.01). IHC analysis also revealed that LIF was highly expressed at protein level(P < 0.05) and mainly seen in the cytoplasm of endometrium glandulose cells. Conclusion:These results indicated that YiKang decoction may cure the infertily through increasing expression of LIF in the endometrium.