The black discharge after menstruation may be residual menstrual blood, or it may be caused by stale bleeding, which is not clean. 1. Residual menstrual blood: Because there are many folds in the female vagina, there is a small amount of menstrual blood hidden in the folds of the vagina, when the body position changes or exercise, the residual menstrual blood in the folds along with the cervical mucus and shedding of vaginal epithelial cells out of the body, due to the residual time is long, so it may be manifested as a blackish-brown secretion. 2. Stale bleeding: there are many causes of stale bleeding, common causes include endometritis, endometrial polyps, cervical polyps, severe cervical erosion, cervical cancer and so on. 3. Others: It may also be due to eating too much cold food during menstruation which leads to dribbling of menstrual blood, darker color, stale bleeding and so on. If you find dark brown discharge after menstruation once in a while, it is usually not a big problem, but if it occurs frequently, you should go to the hospital for a more comprehensive examination.