Objective To investigate the alteration in the expression of DNA methyltransferase 1(DNMT1) and histone deacetylase 1(HDAC1) in endometrium from women with endometriosis and to explore the effects of both DNMT1 and HDAC1 on the endometriosis. Methods DNMT1 was localized with immunohistochemistry，DNMT1 and HDAC1 was quantified with Western blotting in the endometrium of 38 premenopausal women (18 with endometriosis and 20 without endometriosis). Results DNMT1 was predominantly located in the nuclei of glandular epithelial cells and stromal cells. The intensities of the DNMT1 immunohistochemical staining were significantly higher in the women endometrium with endometriosis than those without endometriosis(EM>P/EM><0.01）. DNMT1 and HDAC1 protein levels in the endometrium of women with endometriosis were significantly higher than those without endometriosis throughout the menstrual cycle（EM>P/EM><0.05）. There was a positive correlation between endometrial DNMT1 and HDAC1 levels in the endometriosis（EM>P/EM><0.05）.Conclusion High expression of DNMT1 and HDAC1 in the endometrium sug