The gp90 protein of REV is an important antigenic protein and is associated with virus neutralization, which is the major candidate antigen for vaccine development and disease serological diagnosis [12, 13] . Studies showed that recombinant gp90 protein expressed in Pichia pastoris induced a protective immune response against REV in chickens [19] . Precise mapping of epitopes in gp90 is important for understanding antibody-mediated protection and developing epitope-based marker vaccines and diagnostic tools. Cui et al. [20] reported the generation and partial characterization of a panel of 11 mAbs against the nondefective REV Strain T, and showed that the epitope was on the viral envelope glycoprotein. However, they only identified the relative regions in REV envelope glycoprotein recognized by the mAbs, and did not map the fine locations of the epitopes. To our knowledge, there has been no report on linear epitope mapping of the gp90 of REV.