A method for inhibiting proliferation of Helicobacter pylori including a compound that can simply be mass-produced, can specifically inhibit the proliferation of H. pylori, which has high safety and never generates any resistant bacteria, as well as a diet of a food or beverage, and a pharmaceutical preparation containing the proliferation inhibitor of Helicobacter pylori. The proliferation inhibitor of Helicobacter pylori comprises an alpha-N-acetyl-glucosaminyl bond-containing monosaccharide derivative represented by the following chemical formula (1) GlcNAc1-alpha-O—Y   (1) (in the formula (1), Y is a straight-, branched- or cyclic-aliphatic hydrocarbon group having 1 to 27 carbon atoms or a straight-, branched- or cyclic-acyl group having 1 to 27 carbon atoms). The diet of the food, the beverage or the pharmaceutical preparation comprises the proliferation inhibitor of Helicobacter pylori.