Ovarian pain on one side during menstruation may be caused by estrogen changes, adnexitis and pelvic inflammatory disease. 1. Estrogen changes: the patient’s estrogen level changes during menstruation, stimulating the patient’s abdominal nerves, appearing on one side of the ovary slight pain. 2. Adnexitis: Adnexitis is a kind of gynecological disease, usually not very painful, to the menstrual period, the pain will be more obvious, will also appear during menstruation, one side of the ovary will be painful performance. 3. Pelvic inflammatory disease: the feeling that one side of the ovary will be painful during menstruation may also occur. Patients in the phenomenon of one side of the ovary during menstruation pain, it is recommended to go to the regular hospital gynecology examination, once diagnosed to timely treatment.