Objective: To prepare the surface immunogenic protein(Sip) of group B streptococcus(GBS),study its immunogenicity and function and lay a foundation of development of GBS protein vaccine. Methods: Construct expression vector by gene recombination technique and express GP-Sip. Immunize mice and rabbits with previously expressed pET-Sip. Identify the specificity of expressed GP-Sip by Western blot with the antisera of immunized rabbits. Determine the specific antibodies in sera of immunized mice and rabbits by ELISA using the expressed GP-Sip. Determine the function of Sip antiserum by opsonophagocytosis test in mice. Results: Expression vector was correctly constructed as proved by restriction analysis and sequencing. GP-Sip was expressed in a soluble form in E. coli, and reached a purity of more than 90% after purification. Western blot showed specific reaction of GP-Sip with antisera against pET-Sip. ELISA proved that Sip induced high serum IgG level in mice. Sip antiserum promoted the phagocytosis of GBS by phagocytes significantly. Conclusion: The expression vector for GP-Sip was successfully constructed, and Sip was highly expressed. The expressed product showed good immunogenicity, and its antiserum showed good protection, which might be a candidate component of GBS protein vaccine or vector of capsular polysaccharide vaccine.