Objective: To explore the possible mechanism of Yishen Zhongzi Pills （YSZZP） in treatment of unexplained infertility by observing the effects of YSZZP on E-cadherin expression in endometrium at mid-lutein phase in unexplained infertility patients. Methods: E-cadherin expression in endometrium at mid-lutein phase was respectively determined in 45 cases of unexplained infertility patients （research group of 30 cases and control group of 15 cases） and 17 cases of healthy women by using immunohistochemical method. Research group was given YSZZP for 3 months

and the control group was given sexual life instruction based on monitoring ovulation. E-cadherin expression was re-examined after treatment course finished. Results: E-cadherin expression was weak positive in unexplained infertility patients

and was strong positive in healthy women

with significant differences （P<0.01）. E-cadherin expression significantly increased after treatment in research group （P<0.01）. Conclusion: E-cadherin expression deficiency in endometrium at mid-lutein phase might be one of the causes of infertility

and increase of E-cadherin expression by YSZZP might be the mechanism of treatment of infertility.