Abstract: In order to explorer the pathogenicity, two enteroeoecus strains isolated from ducks were respectively inoculated into white mice, the clinical signs and pathological changes were observed, and the morbidity, mortality and 50 % lethal dose （LD50） of the strains to mice were determined. The results showed that the two enterococcus strains were both virulent to mice. The liver, kidney and spleen of the mice were damaged. The most obvious pathological features were as follows： splenomegaly and fibrinous exudate were seen in spleen; congestion, hemorrhage and even necrosis presented in liver; renal interstitial vascular congestion also could be seen. Those results indicated that enterococeus strains can infect mice and cause tissue damage and death.