Gastric colonization of Helicobacter pylori (H. pylori) occurs in a very early age via infected mothers having H. pylori-specifi c IgG antibodies that would be transplacentally transferred to infants. In addition, H. pylori urease-specifi c IgG was associated with chronic gastric atrophy and post-immunization gastritis is usually correlated with a strong local IgG response. These fi ndings indicate that H. pylori-specifi c IgG antibodies, in particular its urease-specifi c IgG, may induce unfavorable infl uence on host resistance against H. pylori. Here, we show that we have found a unique H. pylori urease-specifi c IgG monoclonal antibody (MAb), termed S3, recognizing the conformational structure of the small subunit Ure-A, which enhanced the urease enzymatic activity.