The mouse model is alleged to be a useful tool for understanding of pathophysiological roles of Helicobacter pylori in the development of gastric disorders. However, it has been observed that H. pylori strains significantly differed in their fitness in mice and even mouse strains differed in their susceptibilities to a H. pylori strain. Bacterial components of H. pylori which could affect on its fitness in mice have to be elucidated for the establishment of the mouse model for H. pylori infections. In the comparison of colonization ability between two H. pylori Korean isolates, 51 (isolated from a patient with duodenal ulcer) and 52 (isolated from a patient with gastric cancer), 52 could colonize better than 51 on the gastric mucosa of mouse. Proteome components of H. pylori 52, as a good colonizer and H. pylori 51, as a poor one were quantitatively compared each other. Five bacterial proteins including catalase, urease subunit alpha/beta, enolase and ferritin, were up-regulated in 52. In addition, the respective proteome components of the two strains were also compared with their mouse-passaged homologous strains. Seven and five proteins, which included catalase, flagellin A/B in common, were up-regulated in mouse-adapted 51 and 52, respectively. Among the fourteen identified proteins, urease subunit alpha/beta, flagellin A/B, catalase, ferritin, superoxide dismutase and neutrophil-activation protein have been previously known to be necessary to gastric colonization of H. pylori in animal models. The other up-regulated proteins including enolase, elongation factor Tu and fructose-bisphosphate aldolase have been reported to be associated with acid tolerance of H. pylori. These data provide confirmatory evidence for the importance of those proteins in the development of H. pylori-associated gastric disorders.