Objective To investigate the different expressions of purinergic P2X7 receptor in normal endometrium and ectopic endometrium of patients with endometriosis (EMS), so as to discuss the possible role of P2X7 receptor in the development of EMS. Methods The tissue samples (ovarian endometriotic cysts) of EMS patients (EMS group, n=54) and normal endometrium tissues from uterine fibroid patients undergoing hysterectomy (control group, n=40) from Oct. 2011 to Oct. 2012 were retrieved in Changhai Hospital.The expression of P2X7 receptor was detected and compared by immunohistochemistry between the two groups. P2X7 receptor expressions were also compared between patients with different preoperative serum CA125 levels or EMS stage according to intraoperative evaluation by revised American Fertility Society (rAFS) staging. Results (1) The positive rate of P2X7 receptor was 75.9% (41/54, with 22 weakly positive, 14 positive and 5 strongly positive) in 54 EMS samples, which was significantly higher than that in normal endometrial tissues (7.5%, 3/40, all weakly positive)(χ²=43.21, P<0.05). P2X7 receptor expression intensities were also significantly different between the two groups(Z=-7.318, P<0.05). (2) P2X7 receptor expressions in EMS patients with serum CA125 ≥50 U/mL or of Ⅲ-Ⅳ stage (rAFS) were significantly stronger than those with serum CA125 < 50 U/mL (Z=-2.642, P<0.05) or of Ⅰ-Ⅱ stage (Z=-3.815,P<0.001). Conclusion P2X7 receptor is highly expressed in the ectopic endometrium tissue, and the expression is associated with the pre-operation serum CA125 level and severity of disease, suggesting that P2X7 receptor may be involved in the development of endometriosis.