Abstract: Objective：To study the methylation alteration in menstrual proliferative and secretory period of endometriosis through testing the expression level of DNMT1 and DNMT3B in serum and peritoneal fluid. Methods：Choose the women received the hysteroscopy-laparoscopy surgery in Peking University Shenzhen Hospital from July 2013 to December 2013. The study group divided by 61 cases of endometriosis （EMs）, with 39 cases of Ⅰ-Ⅱ stages (group A) and 22 cases of Ⅲ-Ⅳ stages (group B). The control group divided by 27 cases of no-endometriosis (group C). Use the enzyme linked immunoabsorbent assay method to test DNMT1 and DNMT3B expression level in serum and peritoneal fluid. Results：①In the proliferative period，group B had higher DNMT1 expression in serum than group A and C, group A and B had higher DNMT3B expression in serum than group C, both with a statistically significant difference （P＜0.01）. ②In the proliferative period, group A had higher DNMT3B expression in peritoneal fluid than group B and C, with a statistically significant difference （P＜0.01）. ③In the secretory period, there were no statistically significant difference of DNMTs expression in serum and peritoneal fluid among three groups（P＞0.05）. Conclusions：In the proliferative period，methylation obviously change in EMs，methylation differently change in different EMs stages，indicating that the DNA methylation alteration in the proliferative period play an important role in the genesis and development of EMs.

Key words: Endometriosis, DNA (Cytosine-5-)-Methyltransferase, DNA Methylation