To evaluate immunohistochemical (IHC) staining of decorin and vascular endothelial growth factor (VEGF) of ovarian and endometrial tissues in patients with and without endometriosis. Study Design: Descriptive study.Department of Obstetrics and Gynecology, ZeynepKamil Training and Research Hospital, Istanbul, Turkey, between Istanbul, TurkeyJanuary 2018 and June 2019.Thirty patients, who underwent total abdominal hysterectomy (TAH) + bilateral salpingo-oophorectomy (BSO)/unilateral salpingo-oophorectomy (USO) and were in the proliferative phase of menstrual cycle,were included. The study population consisted of 20 patients (patient group) with an endometriomaand the control group consisted of 10 patients who were operated for benign gynecological pathologies.The ovarian and endometrial tissue specimens were collected from the archives. IHC staining was performed using decorin and VEGF.Decorin analysis showed a significantly higher intensity of staining in both endometrial and ovarian tissues in control group than patient group. Patients with endometriosis had a lower intensity of staining of decorin and a higher intensity of staining of VEGF compared to control group. There was a negative, statistically significant concordance between VEGF and decorin staining of endometrial tissues of both groups (concordance rate -0.560, p=0.001). Therewas a negative, statistically significant concordance between VEGF and decorin staining of ovarian tissues of both groups (concordance rate -0.564, p<0.001).Angiogenesis plays a critical role in endometriosisand interaction between decorin and VEGF,which suggests that decorin may be a promising molecule for the treatment of endometriosis. Key Words: Decorin, Endometriosis, Immunohistochemical staining, Vascular endothelial Growth factor.