Background: Global estimated prevalence of endometriosis is about 10 to 15% of women in reproductive age. This chronic inflammatory ectopic endometrium causes pain symptoms and is also attributed to infertility problems. Even though advances in endometriosis management have been developed, cumulative recurrence rate of endometriosis is still as high as 55% after 5 years of therapy with GnRH agonist. Therefore, further investigations are continuously needed to improve treatment outcome in endometriosis, especially through better understanding of the disease pathophysiology. Methods: This cross-sectional study was aimed to describe the expression of GnRH receptor type-II (GnRHR-II) with immunohistochemical staining. Semiquantitative analysis of protein expression was performed with histological scoring (H-score). Moreover, the expression level of GnRHR-II was then compared to Ki-67 protein expression, a marker of cell proliferation. Results: We found a positive correlation between GnRHR–II expression with Ki–67 protein (Pearson correlation score 0.56, 95% CI: 0.15–0.80, p = 0.01). Interestingly, our results also found that the expression of GnRHR–II was also significantly higher in groups of subjects with larger endometriosis tissue size (p = 0.02). Conclusion: Our study showed an evidence of extrapituitary expression of GnRH receptor type-II. Endometriosis consistently expressed GnRHR-II and might play important role in the regulation of proliferation. Our results may trigger further explorations of GnRH receptor-targeted therapy that selectively inhibit proliferation pathway.