Based on an established rhesus monkey model , an entrovirus 71 ( EV71) challenge study was conducted. Responses to viral inf ection were determined following immunization with an inactivated vaccine . All three vaccine doses ( 20 , 80 and 320 EU) induced neutralizing antibody responses in rhesus monkeys . Inthe 80 EUand 320 EUgroups , titers of 1∶128-1∶256 were detected at week 4 after the boost vaccination. After intranasal challenge with 104 .5 CCID50 EV71 , viral load was negative in blood, central nervous system( CNS) , and other organs . Inthe 20 EUgroup , al ow viral load could be detectedin blood , lymph nodes , CNS, and other major organs . The pathol ogical results showed that there was no obvious  damage in the CNS, lung and other organs in all three dosage groups . The findings suggest that this experi mental EV71 vaccine can protect the monkeys fromviral challenge .