Basing on the previous studies of elicited protection in mice and rhesus monkeys, a formalin-inactivated EV71 vaccine (Human Diploid cell, KMB-17 Cell) has been licensed by SFDA in China, Dec. 2010. The phase I clinical and phase II trials were completed, in Guangxi Province, China. The results of these clinical trials showed that this vaccine was safe and could induce effective antibodies for the infants. The purpose of phase III is to evaluate the protected and efficacy of the formalin-inactivated EV71 vaccine in Chinese infants and children (from 6 to 71 months old).