Abstract: The immune response of soft-sshelled turtle, Pelodiscus sinensis Wiegmann, was influenced by different immunogens and their doses. In comparison with other five strains, the immunogenicity of strain T3 was the highest, and its optimum immunization doses were 50～100 ×108 cfu / ml within which the percent relative protection (PRP) and serum indirect agglutination titer(IAT) reached higher levels.Below or above these doses the level of immune response was lowered to a certain degree. When more than 160 ×108 cfu/ml, the formation of a state of tolerance was observed, in which the turtle failed to response to a normal immunogenic dose. It was demonstrated that water temperature of 25～30℃ was optimum to provoking the immune response of the turtle and below 10℃ the response was weakened greatly.In addition, better water quality and sunshine are important factors for increased immune response level of the turtle.