OBJECTIVE To evaluate the safety and immunogenicity of group A/C meningococcal polysaccharide conjugate vaccine. METHODS The double-blind, randomized, parellel controlled, single central clinical trial was carried out to evaluat safety and immunogenicity of MCV-A/C. RESULTS 4-fold rise rate of antibody to group A, C and A/C were more than 90 percent after MCV. The GMTs of antibody serogroup A and C were more than 1:150 in four trial groups aged 3-5 months, 6-23 months, 2-15 years and 16-30 years, for which the susceptive subjects seroprotected. There were no significant differences between MCV and the control group in the systemic and local reactions rates. The systemic and local reactions rates after the first, second and third dose of MCV were low. And no severe systemic and local reactions. CONCLUSIONS Group A/C MCV was safe and immunogenic for the population > or =3 months old. Registration National Food drugs Surveillance administrative bureau, Medicine Clinical Experiment Written Directive from a superior" number:2006L04776.