Background: Brain-derived neurotrophic factor (BDNF) has been recognized as a regulator in the formation and maintenance of chronic pain in various chronic disorders. BDNF together with its high-affinity tyrosine kinase type B (TrkB) receptor were found to be extensively expressed in mammalian female reproductive system. However, BDNF and TrkB expression in different stages of endometriosis, and the correlation between their expression in ectopic lesions and endometriosis pain remains unclear.Methods: This study enrolled sixty-two women underwent laparoscopic surgery. Forty-six women diagnosed as ovarian endometrioma, were recruited in the study group. Sixteen women diagnosed as ovarian benign tumors were recruited in the control group. Samples from eutopic endometrium and ovarian endometriotic lesions were obtained at laparoscopic surgery. The message RNA (mRNA) level of BDNF and TrKB was detected by real-time PCR, while the protein level was detected by immunohistochemical staining for eutopic and ectopic endometrium in both groups. Dysmenorrhea was assessed by the visual analogue scale (VAS) before the surgery.Results: The expression of BDNF and TrKB were higher in ovarian endometriotic lesions than those in eutopic endometrium and normal endometrium (P<0.05), and there was no cyclical change. While their expression in eutopic endometrium were higher than those in the normal endometrium (P<0.05). The expression of BDNF and TrKB in ovarian endometriotic lesions stage IV were higher than those in stage III and II (P<0.05). Their expression in stage III were higher than those in stage II but there were no significance (P>0.05). Furthermore, the correlation between the mRNA expression of BDNF, TrKB in eutopic endometrium, and dysmenorrhea VAS score revealed that r=0.52 and 0.56, respectively (P<0.05). The correlation between BDNF and TrKB in both eutopic and ectopic endometrium were revealed that r=0.82 and 0.66, respectively (P<0.05).Conclusions: BDNF and TrKB may play essential roles in promoting disease progression during the development of endometriosis, and are closely related to dysmenorrhea caused by endometriosis.