A B-cell activating factor of the tumor necrosis factor (TNF) family (BAFF) is an essential B-cell survival factor. Myasthenia gravis (MG) is one of the most typical antibody-mediated autoimmune disorders. To test whether serum BAFF levels are increased in MG patients, we compared the serum BAFF levels of 40 MG patients with those of 30 healthy controls. Serum BAFF levels of MG group were significantly higher than those of healthy group. These results suggested that the BAFF might play a role in the immunopathogenesis of MG and further study on B-cell and T-cell activation may be needed.