Brucella abortus (B. abortus) is a facultative intracellular pathogen that can survive inside macrophages and trophoblast giant cells, and the causative agent of brucellosis. In the present study, we found that production of regulated upon activation normal T-cell expressed and secreted (RANTES) due to B. abortus infection contributes to abortion in pregnant mice. B. abortus infected pregnant interferon-gamma (IFN-gamma) knockout mice died within 15 days of infection, but non-pregnant IFN-gamma knockout mice were still alive. With infection by wild type B. abortus, a large amount of RANTES production was observed in pregnant IFN-gamma knockout mice, and induction of RANTES was also observed in normal pregnant mice infected with the wild type, but not in those infected with the intracellular replication-defective mutant. Production of RANTES and IFN-gamma were inhibited in mice inoculated with the respective RANTES or IFN-gamma antibody. Neutralization of RANTES, induced by B. abortus infection, served to prevent abortion. These results indicate that the production and function of RANTES are correlated with IFN-gamma in pregnant mice infected with B. abortus.