Understanding the effect of immunosuppressive agents on intestinal microbiota is important to reduce the mortality and morbidity from orthotopic liver transplantation (OLT).We investigated the relationship between the commonly used immunosuppressive agent cyclosporine A (CSA) and the intestinal microbial variation in an OLT model.The rat samples were divided as follows: (1) N group (normal control);(2) I group (isograft LT,Brown Norway[BN]rat to BN);(3) R group (allograft LT,Lewis to BN rat);and (4) CSA group (R group treated with CSA).The intestinal microbiota was assayed by denaturing gradient gel electrophoresis profiles and by using real-time polymerase chain reaction.The liver histopathology and the alanine/aspartate aminotransferase ratio after LT were both ameliorated by CSA.In the CSA group,the numbers of rDNA gene copies of Clostridium cluster I,Clostridium cluster ⅩⅣ,and Enterobacteriaceae decreased,whereas those of Faecalibacterium prausnitzii increased compared with the R group.Cluster analysis indicated that the samples from the N,I,and CSA groups were clustered,whereas the other clusters contained the samples from the R group.Hence,CSA ameliorates hepatic graft injury and partially restores gut microbiota following LT,and these may benefit hepatic graft rejection.