Abstract： Objective　To investigate the effects of mifepristone on expression of estrogen receptor (ER) and progeserone receptor (PR) in cultured human eutopic and ectopic endometria. Methods　Endometrial (n=22) and endometriotic (n=12) tissues，obtained from patients with endometriosis, were cultured with and without mifepristone (1×10-6 mol/L，1×10-4 mol/L) for 7～10 days. The expressions of ER, PR were determined by semi-quantitative immunocytochemistry method. Thirteen normal endometrial samples served as controls. Results　The expressions of ER and PR in normal and eutopic endometrial cells showed the same cyclic pattern. The only difference was the significantly higher PR glandular content in eutopic endometria of endometriosis patients ,as compared with normal controls ［histochemistry score (H-score) 2.77±0.32 Vs 2.20±0.26 P<0.05］. On the contrary, the ER, PR expressions in ectopic endometrial cells were significantly lower only during the proliferative phase (ER: gland 0.65～2.17 Vs 1.50～3.23, stroma 0.45～1.03 Vs 0.80～1.96; PR: gland 0.55～1.77 Vs 1.55～3.34, stroma 0.40～1.27 Vs 0.98～2.50; P<0.05～0.01); significantly higher only during the late secretory phase (ER: gland 3.27±0.31 Vs 0.28±0.11, stroma 1.87±0.31 Vs 0.26±0.15; PR: gland 3.33±0.23 Vs 0.36±0.23) as compared with those of eutopic endometria.10-6～10-4 mol/L of mifepristone significantly suppressed the expressions of ER, PR in both eutopic and ectopic endometrial cells of endometriosis patients (P<0.01) in a dose-dependent manner. Conclusions　Expression of ER, PR of endometriotic cells differed significantly from that of endometrial cells of patients with or without endometriosis. The down-regulatory effect on ER and PR may be one of the therapeutic mechanism of mifepristone on endometriosis.