Background: Myasthenia gravis (MG) is an autoimmune disease. Evidence has shown that the function of the lymphocyte immune can be regulated by microRNAs (miRNAs). This study aimed to explore whether miR-155-5p can regulate the activation and suppressive function of T-regulating cells (Tregs) in MG. Methods: Blood samples of patients with MG were collected to evaluate the levels of miR-155-5p, BCL10, and the proportion of Tregs. The correlation between the level of miR-155-5p and BCL10 was evaluated in humans. The levels of miR-155-5p and the proportion of Tregs were further detected in the experimental model of autoimmune myasthenia gravis (EAMG). The dual-luciferase reporter assay was used to verify whether miR-155-5p can target BCL10. To reveal the regulatory function of BCL10 to Tregs, CD4+CD25+Tregs were transfected with either si-BCL10 or miR-155-5p inhibitors, and detected by measuring anti-inflammatory cytokines and transcription factors. Results: The level of miR-155-5p significantly increased in MG patients compared to the control group (P<0.001), while the level of BCL10 significantly decreased in MG patients (P<0.001). There was a negative correlation between the level of miR-155-5p and BCL10 (r=0.3292, P=0.0253). The proportion of Tregs significantly decreased in MG patients and the spleen of EAMG rats compared to the control groups (P<0.001; P<0.05, respectively). The dual-luciferase reporter assay showed that miR-155-5p can target BCL10. BCL10 contributed to the activation and immunosuppressive function of Tregs. Conclusions: miR-155-5p inhibits the activation and immunosuppressive function of Tregs by targeting BCL10, which may be a potential target in the treatment of MG.