Abstract: Objective To evaluate the efficacy and compare the decrease of related medical care cost of 23-valent pneumo coccal polysaccharide vaccine in pneum ococcal infection diseases prevention among the elderly people in Beijing.Methods A historic cohort study was conducted.We selected 116 elderly people who vaccined pneum ococcal polysaccharide vaccine during the period of 2005-2008 in Beijing as the vaccined group,and 116 elderly people who did not have vaccine during the same period in the same community as the unvaccined group.The subjects were matched on age,gender,health condition,and income level.Also,we collected base line informationon,incidence of related pneumonia diseases and medical care costs with a questionnaire.Chi-squaretest,Utest and nonparametric test were adop ted in the analy sis.R esu lts The incidence density o f pneum o co cca l infec tion d isea ses and re la ted pneum on ia diseases in the vaccine group and unvaccine group was 9.17/100 person year and 48.42/100 person year,respectively.The protective rate was 81.10% and relative risk (RR) was 0.19,(95% confidence interval CI 0.100.34).The total health economic analysis indicated the cost was 24 418 RMB yuan and the total savings was 458 435.32 RMB yuan.The benefit cost ratio(BCR) was 6.49.BCR was sensitive to the cost of vaccine and the incidence of pneum ococcal diseases.Conclusion The pneumo coccal polysaccharide vaccine has an efficacy and good cost-benefit for prevention of pneum ococcal infection diseases and related pneumonia diseases in the elderly population in Beijing.