Small peptides and oligosaccharides are important antigens for the development of vaccines and the production of monoclonal antibodies. Because of their small size, peptides and oligosaccharides are non-immunogenic on their own and typically must be conjugated to a larger carrier protein to elicit an immune response. Selection of a suitable carrier protein, conjugation method, and hapten density are critical for generating an optimal immune response. We used a glycan array to compare the repertoire of antibodies induced after immunizing with either low or high-density conjugates of the tumor-associated Tn antigen. At high hapten density, a broader range of antibodies was induced, and reactivity to the clustered Tn antigen was observed. In contrast, antibodies induced by the low-density conjugate had narrower reactivity and did not bind the clustered Tn antigen.