Detailed analysis of epitopes is important for the understanding of immunological events, and the development of epitopebased marker vaccines and diagnostic tools for various diseases [14, 15] . In this study, we prepared a neutralizing monoclonal antibody (mAb) against gp90 protein from the REV-A strain HLJ07I, and used it to screen a phage-displayed random 12mer peptide library for the linear B-cell epitope. This study describes the first identification of the precise location of the epitope on gp90 protein. The information provided in this study will facilitate the development of specific serological diagnosis of REV infection, and will contribute to the rational design of vaccines by further understanding of the antigenic structure of gp90.