Authors experienced a case of malignant melanoma of the mediastinum, At the time of first visit to the hospital, the female patient, aged 48, and had chief complaints of right shoulder pain that was radiated to its forearm and right Horner`s syndrome. In chest X-ray and CT, extrapulmonary circumscribed mass in the right apicomedial aspect of mediastinum was found. She had no nevus and no melanoma on entire skin area. We excised the tumor and confirmed it as malignant melanoma by histopathology.