The invention is directed to immunogenic compositions comprising polysaccharides and polysaccharide-protein conjugates that are useful to induce or detect the production of antibodies specific for H. pylori. The invention is also directed to methods of purifying the H. pylori polysaccharides from bacteria. The polysaccharide may be incorporated into an immunogenic composition or used in vitro to assay for the presence of H. pylori antibodies in a sample or biological fluid.