Objective: To discuss the influence of mifepristone to caspase 3 expression in adenomyosis tissue. Materials and Methods: Sixty patients were equally divided into four groups. Groups 1,2, and 3 were treated with 5, 10, and 15 mg mifepristone, respectively and group 4 was treated with placebo. The expression of caspase 3 was examined by immunohistochemical method in both eutopic and ectopic endometria of the 40 cases. Results: Compared with placebo group, the expression of caspase 3 in both eutopic endometrium and ectopic endometrium in the three treatment groups was significantly increased. There was no difference in the expression of caspase 3 in both eutopic and ectopic endometria between the ten and 25 mg treatment groups, while both the ten and 25 mg treatment groups had a higher expression intensity of caspase 3 in both eutopic and ectopic endometria, compared with the five mg treatment group (p < 0.01). Conclusion: Mifepristone can increase the expression of caspase 3 in both eutopic and ectopic endometria and initiate cell apoptosis in both eutopic and ectopic endometria. Therefore mifepristone can effectively inhibit the emergence and development of adenomyosis.