Animal studies have indicated an important role of tumor necrosis factor-alpha (TNF-α) in the pathogenesis of myasthenia gravis (MG), and trials of monoclonal antibodies that block TNF-α have shown clinical improvement. However, before a TNF-α blocking agent is proposed for treatment of MG, whether serum TNF-α level correlates with the patient's condition should be confirmed. Therefore, we evaluated the relationship between the serum TNF-α level and clinical factors, including the quantitative MG score and the anti-acetylcholine receptor antibody level, in 33 MG patients. TNF-α levels ranged from 0.44 to 3.63 pg/mL and did not correlate with clinical factors. Overall, we found that serum TNF-α levels varied greatly among MG patients.