To analyze the change of branched chain amino acids (BCAAs) level in peripheral serum of patients with myasthenia gravis (MG), and to explore its immunomodulatory role in the experimental autoimmune myasthenia gravis (EAMG) animal model. Methods: Total 54 MG patients (MG group) and 35 healthy controls (control group) were enrolled respectively. Liquid chromatography - mass spectrometry testing was used to detect the levels of BCAAs, lymphocyte subsets, and cytokines in both groups, and the results were compared. EAMG mice were fed by BCAAs, then changes to muscle strength were evaluated and cytokine levels were detected by ELISA. Results: Compared with those of the control group, the levels of Val and Ile in the MG group were lower, and the levels of TNF-α, IL-6, IL-8 were higher (P<0.05). Compared with normal diet EAMG mice, the BCAA-fed mice showed significantly reduced clinical scores and levels of TNF-α, IL-6, and IL-8 (P<0.05). Conclusion: BCAAs are helpful in improving immune response in MG. Through adjustments to BCAAs metabolism or their transport proteins, a new route for regulating immunity in MG may be established.