To develop a vaccine candidate virus for EV71, the authors have used ten EV71 viruses were provided by IP Hochiminh. First step, three times of viral propagation were perfonned by using Vero cells, resulting in a highest titer virus was selected (VN06-278NH-RD4 (EV-04)/6,62 log 10 CCID50/ml). Next step is cloning by dilutionbase method for three times and the EV04.12.38.76 virus was selected as a candidate vaccine virus for EV71. Last step is checking stabilization of antigen by a serial passages method (30 times), the authors found that the EV04.12.38.76 virus is introducing a titer ranger from 5.75 to 7.62 log 10 CCID50/ml. The results might provide an adequate procedure for vaccine candidate virus selection for EV71 or others. To develop vaccine seed viruse of EV71, the authors used 10 strains of EV71 provided by Pasteur Intitute of Ho Chi Minh city. Beginning the viruses were propagated in vero cell three times. The VN06-278NH-RD4 (EV-04) reached titer 6,62 log 10 CCID50/ml was selected for cloning. After 3 times cloning, EV04.12.38.76 clone was chosen for next step. The virus strain were passage 30 times in vero cell. The result showed that virus propagated well with the titer range from 5.75 to 7.62 1og 10 CCID50/ml.