Objective:To investigate the immune mechanism of Shengxian decoction in experimental autoimmune myasthenia gravis(EAMG) rats. Methods:Lewis rats were immunized with the rat sequence 97-116 of the AChRαsubunit(Rα97-116) in CFA, 25 of which were successful. They were randomly divided into 5 groups:EAMG model group,prednisone group(5. 4 mg/kg),Shengxian decoction low, medium, high dose groups ( dosage 2. 6 g/kg, 5. 2 g/kg, 10. 4 g/kg ) . Clinical symptoms, weight, and the decrement percentage of RNS(5 Hz) were evaluated,and ELISA were adopted to determine the titers of AChR Ab,TGF-β,IFN-γ,IL-2,IL-4 and IL-17 in serum. Results:After molding,the percentage of decrement of RNS in each group noticeably increased by more than 10% in comparison with that in the CFA control group ( P<0. 01 or P<0. 05 ) . At the same time, they were also subjected to progressive decreasing weight and typical myasthenia symptoms,showing the successful molding. With medication,the decrement percentage of RNS of rats in the groups with low,medium and high dose of Shengxian decoction were all on obvious decline with alleviated weight decrease (P<0. 01),testifying to the symptom improvement. Compared with the CFA control group,the groups with low,medium and high dose of Shengxian decoction were coupled with decreasing AChR Ab content(P<0. 05),rising TGF-βlevel and reducing IFN-γ,IL-2,IL-4 and IL-17 level(P<0. 01 or P<0. 05). Conclusion: Shengxian decoction can turn the decrement percentage of RNS around,improve the progressive weight decrease in EAMG rats and increase the weight gains. By up-regulating the TGF-βlevel,lowering IFN-γ,IL-2,IL-4 and IL-17 level,preventing B cells from producing AChR Ab and reducing the content of AChR Ab in serum,it will soothe the damage of NMJ to AChR and cure EAMG.