Abstract: Bacterial meningitis caused by different groups of Neisseria meningitidis is still one of the serious health problems world wide. The Serum Bactericidal Assay (SBA) to meningococci is the most important test in immunological evaluation of meningococcal infection after vaccination. The SBA has been adapted as the gold standard for immunity against different serogroups of Neisseria meningitidis after immunization. Capsular polysaccharide of serogroup A meningococci (CPSA) was conjugated to Outer Membrane Vesicle (OMV) from a serogroup B in order to test the possibility of obtaining a bivalent serogroup A and B meningococcus immunogen. The conjugate was prepared with adipic acid hydrazide (ADH) and 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide (EDAC). The conjugate and control were injected intramuscularly into groups of five rabbit with boosters on days 14, 28 and 42 after the primary immunization. The following groups were used as control: 1-CPSA plus OMV; 2-CPSA; 3-OMV and 4-normal saline. The serum collected on days 0, 14, 28, 42 and 56 were tested by complement mediated bactericidal assay according to the world health organization protocol. The results of SBA in the glycoprotein conjugate group revealed a significant increase in serum bactericidal titer against serogroup A meningococci after 56 day in comparison with the CPSA and OMV control group. Bactericidal titer against serogroup B meningococci of the conjugate showed no significant difference in comparison with the OMV containing control. The results indicate that when polysaccharide A and OMV are in a covalent conjugate form, the complex is able to induce a high level of bactericidal antibody response. Therefore, this study shows that the CPSA--OMV conjugate could be a candidate for bivalent vaccine toward serogroup A and B meningococci.