Objective To study the stability of the toxicity,antigenicity and immunogenicity of Neisseria meningitidis serogroup A/C[CMCC(B)29201/29205],and to analyze the quality of the capsular polysaecharide extracted from Neisseria meningitidis.Methods The toxicity of the 3rd,5th,10th,15th,20th,25th and 30th passage of the Neisseria meningitidis was assayed in mice,and the antigenicity of each passage was measured by the tube agglutination test(TAT)and ELISA.The effect of individual 30 passages of Neisseria nveningitidis on the brain tissue and the immunogenicity of each passage were tested in mice,and the capsular polysaccharide was purified and analyzed.Resuits The LD50 of the strains CMCC(B)29201/29205 of each passage was low(≥109/ml),and all the 30 passages of the two strains had no effect on the brain tissue of the mice.The titer of each passage was 1∶320 in TAT and more than 1∶3752 in ELISA.After immunization with individual 30 passages of the Neisseria meningitidis the titers in serum bactericidal assay (SBA)were all more than 1∶32.The capsular polysaccharide purified from Neisseria meningitidis met the quality standard of the requirement.Conclusion The strains of Neisseria meningitidis serogroup A/C used in the manufacture of the meningococcal conjugate vaccine,are stable in the toxicity,antigenicity and immunogenicity.And the capsular polysaccharide has met the quality standard.