Both myasthenia gravis (MG) and Guillain Barré syndrome (GBS) are autoimmune diseases leading to muscle weakness, while the temporal coincidence of MG and GBS is rare. Here, we report a case of MG and GBS, as well as Hashimoto's thyroiditis, for the first time. All these diseases were relieved by immunomodulatory therapy, which suggested abnormal regulation of the autoimmune system might be the cause in our case. In addition, MG was not diagnosed at first from the initial symptom of unilateral lateral rectus muscle palsy.