AbstractExosomes, membrane vesicles released extracellularly from cells, contain nucleic acids, proteins, lipids and other components, allowing the transfer of material information between cells. Recent studies reported the role of exosomes in pathogenic microbial infection and host immune mechanisms.Brucella‐invasive bodies can survive in host cells for a long time and cause chronic infection, which causes tissue damage. Whether exosomes are involved in host anti‐Brucellacongenital immune responses has not been reported. Here, we extracted and identified exosomes secreted byBrucella melitensisM5 (Exo‐M5)‐infected macrophages, and performed in vivo and in vitro studies to examine the effects of exosomes carrying antigen on the polarization of macrophages and immune activation. Exo‐M5 promoted the polarization of M1 macrophages, which induced the significant secretion of M1 cytokines (tumour necrosis factor‐α and interferon‐γ) through NF‐κB signalling pathways and inhibited the secretion of M2 cytokines (IL‐10), thereby inhibiting the intracellular survival ofBrucella. Exo‐M5 activated innate immunity and promoted the release of IgG2a antibodies that protected mice fromBrucellainfection and reduced the parasitaemia ofBrucellain the spleen. Furthermore, Exo‐M5 containedBrucellaantigen components, including Omp31 and OmpA. These results demonstrated that exosomes have an important role in immune responses againstBrucella, which might help elucidate the mechanisms of host immunity againstBrucellainfection and aid the search forBrucellabiomarkers and the development of new vaccine candidates.