Myasthenia gravis (MG) is occasionally associated with other autoimmune diseases. Alopecia areata has been reported to coincide with MG, particularly with thymoma. A 14-year-old woman was diagnosed as having MG. Seven months before diagnosed with MG, her hair and eyebrows had began to disappear and alopecia areata was diagnosed. We report this patient as a rare case of MG associated with alopecia areata without thymoma.