Vaccinia virus recombinants were constructed that incorporated genomic sequences coding for the nucleoprotein (N) and glycoproteins (G1 and G2) of the hantavirus R22 strain isolated from a rat in China, and designated as RNV and RMV9, respectively. The proteins expressed by RNV and RMV9 were identified by radioimmunoprecipitation and indirect immunofluorescence assay using a panel of monoclonal antibodies and polyclonal immune sera, and were found to be antigenically indistinguishable from authentic R22 viral proteins. Both RNV and RMV9 elicited an anti-R22 antibody response in Mongolian gerbils (Meriones unguiculatus) with titers ranging from 6,400 to 12,800 by enzyme-linked immunosorbent assay, but only RMV9 produced neutralizing antibodies to R22 virus (titer 1:200) and Hantaan (HTN) virus (titer 1:20). The ability of these recombinants to protect Mongolian gerbils against challenge with R22 and HTN viruses was examined. The RMV9 recombinant induced a complete protective immune response against challenge with 104 plaque-forming units (PFU) of both R22 and HTN viruses, while RNV induced partial protection against a challenge with the homologous R22 virus and the heterologous HTN virus at a dose of 103 PFU. Our data show that the common antigenic sites responsible for eliciting a protective response are located mainly on hantavirus glycoproteins, and that the nucleoprotein may also confer partial cross-protection that presumably involves cell-mediated as well as humoral mechanisms.