It has been established that purified pneumococcal capsular polysaccharides induce antibody production and such antibody is effective in preventing pneumococcal disease. Clinical studies have demonstrated the immunogenicity of each of the 23 capsular types when tested in polyvalent vaccines. Studies of 23-valent pneumococcal vaccine in children of two years old and older and in adults of all ages have showed immunogenic response. In order to provide more evidence for the immunogenicity and the safety of the vaccine, a phase III clinical trial is planed to conduct.