Objective To investigate the role of tumor suppressor gene PTEN(phosphatase and tension homologue deleted on chromosome 10,PTEN)in apoptosis of ectopic endometrial cells induced by gestrinone. Methods Ectopic endometrium cells obtained from endometriosis were cultured and exposed to gestrinone in different concentrations. The inhibition of the cells during 48 hours was determined by MTT assay, and the cell growth curve was plotted. Then the morphological changes in cells treated with gestrinone for 24h were observed with transmission electron microscope, and the apoptosis rate, cell cycle of the cells and PTEN expression were assessed with flow cytometry analysis (FCM) at the same time. Results Gestrinone in different concentrations could inhibit the growth and proliferation of ectopic endometrium cells in a does and time dependent manner, and the cell growth curve was changed accordingly. After 24 hours exposure to gestrinone in the concentrations of 10 -6 to10 -4 mol/L, some apoptotic changes were observed in the cells under transmission electron microscope. FCM showed that after the exposure to gestrinone, the apoptotic rate of ectopic endometrial cells was 1.3% in 10 6 mol/L group and 15.0% in 10 -4 mol/L group, indicating that there was significantly increase in apoptosis when compared with the control group. At the same time the level of PTEN expression was also increased. Conclusion Gestrinone can significantly inhibit the growth and proliferation of ectopic endometrial cells in endometriosis, and this effects seems to be related to an increase in PTEN expression.