Endometriosis is a common gynecological disease among women of reproductive age, which affects approximately 6 ~10 percent of females, but the pathogenesis of endometriosis is still ambiguous. Until now, the prevailing theory concerning the etiology of endometriosis is the retrograde menstruation hypothesis put forward by Sampson in 1921. However, it can’t illustrate completely the etiology and pathology of the endometriosis. In recent years, immune-inflammatory factor is a hot point of endometriosis field. Many studies demonstrated that the numbers and level of cytokines in the peritoneal fluid of endometriosis patients, namely the macrophage migration inhibitor factor (MIF) which is one of the cytokines described previously, is increased. This has been observed to have a crucial role during the pathology of endometriosis as well as pelvic pain and infertility which are responsible for endometriosis. Therefore, MIF might be the target of new approach to diagnosis and therapy endometriosis.