Objective To explore the mechanism of microRNA (miRNA, miR)-155 in the rejection after liver transplantation in rats. Methods The rats were divided into two groups. In the xenograft model group (rejection group, n=10),the donors were male Lewis rats and the recipients were male BN rats.In the allograft model group(control group, n=10),both the donors and recipients were male Lewis rats.The rat models with orthotopic liver transplantation were established by two-cuff technique in two groups. At postoperative 7 d, the animals were sacrificed for the collection of blood and liver tissue samples. The serum levels of alanine aminotransferase (ALT), total bilirubin (TB), and cytokines of interleukin (IL)-2, IL-4, interferon (IFN)-γ were quantitatively measured. The pathological changes of liver tissues were observed under light microscope. In each group, three liver tissue samples were prepared and subject to high-throughput sequencing. The miRNAs related to rejection were identified for bioinformatics analysis to predict and analyze relevant signaling pathways and genes. Results In the rejection group, the serum levels of ALT and TB were significantly higher than those in the control group (both P<0.01). Compared with the control group, the levels of IL-2 and IFN-γ were considerably up-regulated (both P<0.01), whereas the level of IL-4 was dramatically down-regulated (P<0.01). Pathological examination demonstrated that more evident rejections were observed in the rejection group than the control group. High-throughput sequencing revealed that the expression level of miR-155 was significantly up-regulated in the rejection group, which was 5.89 times of that in the control group. Bioinformatics analysis demonstrated that up-regulation of miR-155 was associated with the mammalian target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK) and T cell receptor signaling pathways. The genes which were probably responsible for regulation included the yeast autophagy related gene 1(ATG1) and its homologous gene ULK2, insulin-like growth factor-1 (Igf-1) and G protein-coupled receptor regulatory gene(Arrb1),etc.Conclusions miR-155 might promote the incidence and progression of rejection after liver transplantation in rats. The involved signaling pathways probably include the mTOR, MAPK signaling pathway and T cell receptor signaling pathway.ATG1,ULK2,Igf-1,and Arrb1 genes may participate in this process.