Bacterial capsular polysaccharides covalently linked to an appropriate carrier protein represent the best tool to induce a protective immune response against a wide range of bacterial diseases, such as meningococcal infections. We describe here the physico-chemical characterisation of glycoconjugate molecules designed to prepare a vaccine against Neisseria meningitidis serogroups A, C, W135 and Y. The use of a selective conjugation chemistry resulted in well characterised, reproducible and traceable glycoconjugate that can be consistently manufactured at large scale. A pool of physical and spectroscopic methods was used to establish glycosylation ratio, identity, molecular weight profiles, integrity of carrier protein and sites of glycosylation, assuring effective and consistent lots of vaccines.