Some factor expected to have an important role in endometriosis pathogenesis; there are immune cell that plays an important role in reception and rejection of endometrial cells that have reflux. Woman with endometriosis with cellular immune disorder (Natural Killer cell, Macrophages, Lymphocytes, and Apoptosis). It is suspected that decrease of NK cell in peritoneal fluid caused by its qualitative defect. CD107a expression is the best validated NK cells marker. The aim of this study was to compared Natural Killer Cell activity expressions with CD107a between endometriosis and non-endometriosis. An analytical case-control study was performed from March until July 2015 in Department of Obstetrics and Gynecology Faculty of Medicine, University of Sumatera Utara, Haji Adam Malik General Hospital Medan. The Case Group was ectopic endometrial tissue block paraffin from endometriosis patient and control group was normal endometrial tissue block paraffin from non-endometriosis group. Proportion analysis of NK cell expression activity used the Quantitative Methods Score/Proportion Score. This study include 23 patients in endometriosis group and control group respectively. Endometriosis group mostly is less than 30 years old (43.5%) and control group is 30-40 years old (52.2%). Endometriosis group mostly on severe stage (47.8%). Statistical analysis showed that there was significant difference in endometriosis tissues with CD107a proportional expression between endometriosis group and control group (p<0.05). Expression of Natural Killer cell activity with CD107a in endometriosis was significantly different compared with non-endometriosis. It suggested that cellular immune factors may play a role in the pathogenesis of endometriosis.