Abstract: Rejection has constantly been an unresolved challenge in the field of organ transplantation. The research on the mechanism of rejection plays a significant role in improving the efficacy of organ transplantation and enhancing the survival rate of graft. The innate and specific immune responses of the human body jointly participate in the graft rejection, leading to graft injury. In recent years, multiple researchers have conducted in-depth studies on the mechanism underlying the role of microRNA (miR) in regulating rejection. Among them, miR-155 has been widely considered as a key factor involved in immune regulation. The expression level and functional status of miR-155 may be intimately associated with the occurrence of rejection, which may become a new target for overcoming rejection. In this article, relevant studies on the role of miR-155 in regulating key immune cells in innate and specific immune responses were reviewed, aiming to provide novel ideas for the development of new immunosuppressants and rejection therapy.