Abstract: 【Abstract】 Objective: To explore effect of aromatase inhibitor on the expression of survivin and Caspase-3 in ectopic focus through establishing rat model of endometriosis . Methods: Rat model of endometriosis was made by way of autologous transplantation of endometrium and 3 weeks later we observed and measured the shape and size of the ectopic foci in abdominal cavity，calculation of volume. Rats were randomly divided into two groups ( twenty in each): Letrozole group and physical saline group as control（NS）. After 4 weeks of administration we observed endometrial histological changes of the two groups and normal rats which were only imposed to abdominal switches surgery without transplantation .Expression level of survivin and Caspase-3 were assessed by immunohistochemical staining in ectopic endometrium and normal endometrium. Results: we successfully established the rat model of endometriosis.After 4 weeks of administratio ,the size of ectopic focus in Letrozole group was reduced and the differences were statistically significant (P <0.05);and both survivin and Caspase-3 were expressed in endometrial glandular epithelial cells, locating in cytoplasm. Results showed that positive rate of survivin in the letrozole group and the normal endometrium group were lower than saline control group and the differences were statistically significant (P <0.01) while there was no difference between the letrozole group and normal endometrial cells (P>0.01); Positive rates of caspase-3 in the letrozole group and the normal endometrium group were higher than saline control group and the differences were statistically significant (P <0.01), while there was no difference between the letrozole group and normal endometrial cells (P> 0.01); The expression of survivin is negatively correlated with that of Caspase-3（r=-0.538，P<0.05）.Conclusion: The aromatase inhibitor can inhibit the growth of ectopic focus and survivin expression and increase expression of caspase-3 in rat ectopic endometrial lesions .The results may offer theoretical foundation for clinical application of letrozole in treatment of endometriosis .

Key words: endometriosis, aromatase inhibitor, rat, survivin, caspase-3