Objective To explore the virulence of enterovirus 71 from infected children in neonatal mice. Methods Three strains of EV71 were isolated from the mild, severe and dead patients. Symptoms, weight and death of mice were recorded throughout 14 days. The mice were sacrificed on the first, third, fifth, seventh and ninth days post infection to gain the tissue virus load including the liver, spleen, lung, intestine, brain and muscle tissue which were used to detect the virus tilter by real?time RT?QPCR, and pathological lesions using HE staining. Results < /b> As to the severity of symptoms, no significant difference was found between the severe and mild groups ( P =0.693), which were more serious than that of the fatal group. ( P = 0.000 < 0.05/6, P = 0.000 < 0.05/6). The survival rate of the mice with mild, severe and fatal virus infection was 77.2%, 81.7% and 97.8%, respectively, and there was a significant difference among the three groups ( P =0.0010 < 0.05, P =0.001 < 0.05, P =0.0004 < 0.05). Lung hemorrhage of the mild group was the most serious, and there were no significant differences in pathological lesions of the brain, muscle, spleen and intestine. Virus titer in the liver and muscle was higher than the other tissues and that in mild group of different tissues tended to be higher than the other two groups. Conclusions Neonatal mice infected with the mild strain of enterovirus 71 presents heaviest symptoms, which are not consistent with the outcomes of humans. It is considered to be related to the virus gene, host and other factors.