In the present study, we demonstrated the utility of the nonmammalian model system Galleria mellonella for studying the pathogenesis of Staphylococcus aureus infection. By use of clinical and laboratory strains that had been exposed to vancomycin, we showed that both agr functional status and vancomycin minimum inhibitory concentration are determinants associated with the virulence of S. aureus in G. mellonella. These results show that G. mellonella can be effectively used to facilitate the in vivo study of S. aureus virulence and, more specifically, the relationship between antibiotic drug resistance and the pathogenesis of infection.