Helicobacter pylori is a chronic infectious agent as defined the major pathogen causing gastritis, gastric and duedonal ulcer, gastric carsinoma and mucosa associated lenfoid tissue (MALT) lymphoma. H. pylori is the only microorganism known to inhabit the human stomach and lining the gastric mucosal cells. Cellular characteristics such as the high motility, the profuse production of urease and the expression of surface lectins play a role in colonizing to human stomach. In this review article, the colonization of H. pylori to stomach mucosa and the importance and the role of urease enzyme in this colonization have been discussed.