Porphyromonas gingivalis（P.gingivalis）, the principal organism associated with periodontal disease, is a Gram-negative, anaerobic and nonmotile bacterium. It has been reported that many bacterial structures of P.gingivalis can induce human immune response which leads to tissue damage and establishment of periodontal disease. P.gingivalis can synthesize and secret polysaccharide which encapsulates bacterial cell wall to form a capsular structure. It has been confirmed that the capsular polysaccharide（CPS） involves in P.gingivalis-induced host immune response to serve as an important virulence factor of this pathogen. According to the K-antigen of CPS, P. gingivalis can be devided into six serotypes, K 1 -K 6 . This review focuses on CPS structure and immunogenicity of P.gingivalis.
