Construction and characterization of mouse monoclonal antibodies against western equine encephalitis virus (WEE) for potential use in detection, diagnosis, and immunotherapy are disclosed. Antibodies were prepared from hybridoma cells and further characterized by ELISAs, Western blotting, isotyping, and immunoprecipitation. The antibodies were also tested for cross-reactivity to other alphaviruses, such as Sindbis virus (SIN), Venezuelan equine encephalitis virus (VEE), and eastern equine encephalitis (EEE). All antibodies bound to WEE antigen in ELISAs, whereas only a subgroup of antibodies was found to be active in Western blotting and immunoprecipitations. A subset of antibodies was found to cross-react with other alphaviruses, such as SIN, VEE, and EEE.