Objective To analyze the relationship between tumor necrosis factor-alpha (TNFo) gene promoter -308 polymorphism and myasthenia gravis (MG) in Chinese and analyze secretion of TNFo in peripheral blood mononuclear cells (PBMC) in MG patients.Methods A biallelic polymorphism at position -308 in the promoter of TNFα gene was screened by PCR amplification and NcoI recognition site. One hundred and twenty-three MG cases and 115 healthy controls were included in this study. MG patients were classified to different groups according to clinical type, age at onset, and sex respectively. PBMC were isolated from 20 patients and 20 healthy controls, and then cultured in the presence or absence of phytohemagglutinin (PHA) and acetycholine receptors (AchR). The supernatants were harvested after incubation and stored until TNFαwas assayed by enzyme-linked immunosorbent assay.Results The frequency of TNFα-308 allele 2 (A) was found significantly increase in MG patients and showed a trend especially in late onset (≥ 40 years) and male patients (P ＜ 0.05). The allele A had no relationship with thymic pathogenesis in MG patients. But frequency of allele A was significantly higher in general type than in ocular type (P ＜ 0.05). MG patients had a higher inducible level of TNFα by PHA and AchR, and could be down regulated after treatment.Conclusion Polymorphism in TNFα gene promoter -308 is associated with onset of MG. The microsatellite allele TNFα2 confer risk for the development of MG in Chinese patients. MG patients have a higher inducible level of TNFα.