Mapping epitopes using monoclonal antibodies has become a powerful tool to study protein structure and has been used to diagnose diseases and design marker vaccines [21, 22, 23] . In this study, we described the generation and epitope mapping of a gp90 protein specific mAb, and demonstrated that the epitope was conserved among the REV group. Precise analysis of REV-A gp90 protein epitope will provide the fundamental information for development of epitope-based vaccines and diagnostic tools for REV-A and/or other REV group infection.