Objective：To study the effects of Streptococcus pneumoniae（S.pn） capsular polysaccharide（CPS） on acute otitis media of C57BL/6 mice. Methods：TIGR4Δcps strain was built by homologous replacement construction. Wild TIGR4（5 ?滋l/ear） or TIGR4Δcps was respectively inoculated into bilateral ear cavity by puncturing the tympanic membrane；an equal amount of sterile phosphate buffered saline（PBS） was injected into the control group. The status of mice was detected every day；inflammation of middle ear ep－ithelia that deal with wild TIGR4 or TIGR4Δcps was observed through HE staining on 1，3，5 d after inoculation. The role of CPS in cell recruitment and bacterial clearance was observed by cell counts and clonal formation unit counts，and the inflammatory cytokines in the middle ear lavage fluid（MELF） were measured to compare the level of inflammation. Results：TIGR4Δcps mutant strain was con－structed successfully. Compared with those of TIGR4 group，mice inoculated with TIGR4Δcps showed lighter damage of middle ear epithelial，lower level of TNF-α and IL-6 in MELF（1 d：P=0.076，P=0.000；3 d：P=0.002，P=0.003；5 d：P=0.000，P=0.000），fewer recruited neutrophils（1 d：P=0.004；3 d：P=0.000；5 d：P=0.000），and faster bacterial clearance（1 d：t=2.659，P=0.029；3 d：t=3.717，P=0.006）. Conclusion：In the mice model of S.pn induced acute otitis media，CPS exacerbates inflammation and tissue injury，and delays clearance of bacteria.