The study was designed to assess in vivo the effects of capsular polysaccharide (CPS) antigen of K. pneumonia on some immunological parameters in albino mice. CPS antigen from K.pneumonia was prepared, then series concetration of wild type of bathogenic bacteria and from CPS antigen were prepared depending on LD50 value which was;1×103 cfu /ml of wilde type and 1×105 cfu/ ml of CPS antigens ,these concentration injected in 0.1 ml intraperetonial in mice . (phagocytosis , Arthus reaction , delayed hypersensitivity and plaque forming cells ) by use two concentration LD50 and 0.1 LD50 which was( 1×105 , 1×106) cfu/ ml in 0.1 ml from CPS antigens« to evaluate the best concentration in stimulate immune response» and bacterial suspention in 3 mice to each test in addition to control group injected by normal saline . The results of this study confirmed that , the CPS antigen in1×106 cfu/ ml concentration after 14 days from injection is the best efficient and gave highest mean in phagocytosis , delayed hypersansativity and arthus reaction , specific immunity in term of plaque forming cells was significantly increase in 1×106 cfu/ ml .It is concluded that efficient immune response can be obtained by CPS from K. pneumoniae
